diff --git a/crates/ui-egui/src/dialogs.rs b/crates/ui-egui/src/dialogs.rs
index 546a386d..9c1e0d30 100644
--- a/crates/ui-egui/src/dialogs.rs
+++ b/crates/ui-egui/src/dialogs.rs
@@ -572,7 +572,8 @@ impl Dialog {
                 _ => None,
             });
         }
-        // With nothing pre-selected, a single profile in the sketch being used is taken.
+        // With nothing pre-selected, a single profile in the sketch being used is taken (#684:
+        // not one a feature already builds from).
         if matches!(d.kind, Kind::Extrude { .. } | Kind::Revolve { .. })
             && let Some(inp) = d.inputs.first_mut()
             && inp.items.is_empty()
@@ -785,16 +786,25 @@ impl Dialog {
     }
 }
 
-/// Profiles of the sketch a feature would use (active, else the last), when there is just one.
+/// Profiles of the sketch a feature would use, when there is just one: the active sketch's, else
+/// the last sketch's while no feature builds from it yet. A used profile (a cube's sketch on its
+/// bottom face) is only taken when it is picked.
 fn default_profiles(s: &Session) -> Vec<Sel> {
     let st = s.world_state();
-    let sid = s.active_sketch.or_else(|| s.doc.features.iter().rev().find(|f| matches!(f.kind, FeatureKind::Sketch { .. })).map(|f| f.id));
+    let sid = s.active_sketch.or_else(|| {
+        s.doc.features.iter().rev().find(|f| matches!(f.kind, FeatureKind::Sketch { .. })).map(|f| f.id).filter(|&id| !profiles_used(s, id))
+    });
     match sid.and_then(|id| st.sketch(id).map(|ss| (id, ss.profiles.len()))) {
         Some((id, 1)) => vec![Sel::Profile { sketch: id, index: 0 }],
         _ => Vec::new(),
     }
 }
 
+/// Does a feature build from this sketch's profiles (extrude, revolve, sweep, loft, emboss…)?
+fn profiles_used(s: &Session, sketch: u64) -> bool {
+    s.doc.features.iter().any(|f| f.kind.profile_sels().iter().any(|(id, _)| *id == sketch))
+}
+
 /// The plane of a planar body face: (point on it, unit normal).
 pub fn planar_face(s: &Session, body: &str, face: usize) -> Option<(Vec3, Vec3)> {
     let st = s.world_state();
diff --git a/crates/ui-egui/src/preselect_tests.rs b/crates/ui-egui/src/preselect_tests.rs
index 5444b772..051248b6 100644
--- a/crates/ui-egui/src/preselect_tests.rs
+++ b/crates/ui-egui/src/preselect_tests.rs
@@ -333,6 +333,97 @@ fn profiles_then_extrude_takes_them_all() {
     assert!(apply_commands(&app, &d).is_ok());
 }
 
+/// #684: with nothing selected, Extrude and Revolve take the last sketch's single profile only
+/// while no feature uses it yet. A cube's sketch lies on its bottom face: taking that profile
+/// again made the dialog default to Cut, so OK cut into the part nobody had picked.
+#[test]
+fn used_profile_of_the_last_sketch_is_not_pre_picked() {
+    let mut h = crate::scenario::Harness::new();
+    let base = h.app.run("sketch.create", json!({"plane":"XY"})).unwrap()["sketch"].as_u64().unwrap();
+    h.app.run("sketch.rectangle.two_point", json!({"p0":[0,0],"p1":[20,20]})).unwrap();
+    h.app.run("sketch.finish", json!({})).unwrap();
+    h.app.run("solid.extrude", json!({"distance":20})).unwrap();
+    h.app.run("select.clear", json!({})).unwrap();
+    let features = h.app.session.doc.features.len();
+    h.call("ui.start", json!({"command":"solid.extrude"}));
+    h.frames(2);
+    let ui = h.call("ui.selection", json!({}))["result"].clone();
+    assert_eq!(ui["selection"], json!([]));
+    assert_eq!(ui["dialog"], json!([{"label":"Profiles","items":[]}]), "the extruded sketch's profile is taken again");
+    let d = h.app.dialog.as_ref().unwrap();
+    assert!(matches!(d.kind, Kind::Extrude { operation: 1, auto_op: true, .. }), "Join, not Cut: {:?}", d.kind);
+    assert_eq!(d.active, 0, "picks go to Profiles");
+    // OK with nothing picked builds nothing: the cube stays whole.
+    h.step(&json!({"key":"Enter"})).unwrap();
+    assert!(h.app.dialog.is_some(), "OK waits for a pick");
+    assert_eq!(h.app.session.doc.features.len(), features);
+    h.step(&json!({"expect":{"bodies":1,"volume":8000}})).unwrap();
+    h.step(&json!({"key":"Escape"})).unwrap();
+    assert!(h.app.dialog.is_none());
+    // Revolve takes the same default.
+    h.app.start("solid.revolve");
+    h.frames(2);
+    assert!(h.app.dialog.as_ref().unwrap().inputs[0].items.is_empty(), "Revolve takes the used profile");
+    h.step(&json!({"key":"Escape"})).unwrap();
+    // A sketch being edited still offers its profile, used or not.
+    h.app.edit_sketch(base);
+    h.frames(2);
+    h.app.start("solid.extrude");
+    h.frames(2);
+    assert_eq!(h.app.dialog.as_ref().unwrap().inputs[0].items, vec![Sel::Profile { sketch: base, index: 0 }]);
+    h.step(&json!({"key":"Escape"})).unwrap();
+    h.app.finish_sketch();
+    // A new sketch on the top face, not used yet, is taken right after Finish Sketch.
+    let top = h.app.run("sketch.create", json!({"plane":{"origin":[0,0,20],"x_dir":[1,0,0],"y_dir":[0,1,0]}})).unwrap()["sketch"].as_u64().unwrap();
+    h.app.run("sketch.rectangle.two_point", json!({"p0":[5,5],"p1":[15,15]})).unwrap();
+    h.app.run("sketch.finish", json!({})).unwrap();
+    h.app.run("select.clear", json!({})).unwrap();
+    h.app.start("solid.extrude");
+    h.frames(2);
+    let d = h.app.dialog.as_ref().unwrap();
+    assert_eq!(d.inputs[0].items, vec![Sel::Profile { sketch: top, index: 0 }]);
+    assert!(matches!(d.kind, Kind::Extrude { operation: 1, .. }), "a boss on the top face joins: {:?}", d.kind);
+    h.step(&json!({"key":"Enter"})).unwrap();
+    assert!(h.app.dialog.is_none(), "{:?}", h.app.dialog);
+    h.step(&json!({"expect":{"bodies":1,"volume":9000}})).unwrap();
+}
+
+/// #684: what stops the pre-pick is a feature building from the sketch's profile (not just an
+/// extrude), anywhere in the timeline; a feature that only follows its curves does not.
+#[test]
+fn profile_use_not_curve_use_stops_the_pre_pick() {
+    // A surface patch fills the sketch's region.
+    let mut app = app_with(json!([
+        {"command": "sketch.create", "params": {"plane": "XY", "name": "Region"}},
+        {"command": "sketch.rectangle.two_point", "params": {"p0": [0, 0], "p1": [20, 10]}},
+        {"command": "sketch.finish", "params": {}},
+        {"command": "surface.patch", "params": {"sketch": "Region"}},
+    ]));
+    assert_eq!(app.session.doc.features.len(), 2);
+    assert!(start(&mut app, vec![], "solid.extrude").inputs[0].items.is_empty(), "the patched region is taken again");
+    // Rolled back to just after the sketch: the extrude after the marker still builds from it.
+    let mut app = app_with(json!([
+        {"command": "sketch.create", "params": {"plane": "XY", "name": "Base"}},
+        {"command": "sketch.rectangle.two_point", "params": {"p0": [0, 0], "p1": [20, 20]}},
+        {"command": "sketch.finish", "params": {}},
+        {"command": "solid.extrude", "params": {"distance": 20}},
+        {"command": "timeline.roll_to", "params": {"position": 1}},
+    ]));
+    let base = app.session.doc.features.first().unwrap().id;
+    assert_eq!(app.session.world_state().sketch(base).map(|s| s.profiles.len()), Some(1));
+    assert!(start(&mut app, vec![], "solid.extrude").inputs[0].items.is_empty(), "the rolled-back extrude's profile is taken");
+    // A pipe follows the circle; the disc inside it is used by nothing.
+    let mut app = app_with(json!([
+        {"command": "sketch.create", "params": {"plane": "XY", "name": "Path"}},
+        {"command": "sketch.circle.center", "params": {"center": [0, 0], "radius": 20, "id": "c"}},
+        {"command": "sketch.finish", "params": {}},
+        {"command": "solid.pipe", "params": {"path_sketch": "Path", "path": ["c"], "diameter": 4}},
+    ]));
+    let path = app.session.doc.features.first().unwrap().id;
+    assert_eq!(app.session.doc.features.len(), 2);
+    assert_eq!(start(&mut app, vec![], "solid.extrude").inputs[0].items, vec![Sel::Profile { sketch: path, index: 0 }]);
+}
+
 #[test]
 fn edges_then_fillet_takes_them_with_chains() {
     let mut app = boxed();