diff --git a/crates/ui-egui/src/documents.rs b/crates/ui-egui/src/documents.rs
index 7ab22a72..be579a94 100644
--- a/crates/ui-egui/src/documents.rs
+++ b/crates/ui-egui/src/documents.rs
@@ -99,7 +99,7 @@ fn swap_in(app: &mut SolveApp, slot: DocSlot) -> DocSlot {
     app.cancel_view_animation();
     app.viewport.orbit_snap = None;
     app.viewport.orbit_free = None;
-    app.preview = crate::preview::PreviewState::default();
+    app.preview.reset();
     app.viewport.hover = None;
     app.menu.props = None;
     crate::sketch_attachment_ui::clear(app);
@@ -199,6 +199,24 @@ pub fn new_design(app: &mut SolveApp) {
     }
 }
 
+/// The tab strip's +: always a new tab, except over the blank design the start page covers
+/// (a launch), which New takes as [`new_design`] does.
+pub fn new_tab(app: &mut SolveApp) {
+    if app.file_picker_busy() {
+        return;
+    }
+    if app.home.open && active_is_blank(app) {
+        new_design(app);
+        return;
+    }
+    app.home.open = false;
+    if let Err(e) = open_tab(app, Session::default()) {
+        app.set_status(e, true);
+    } else {
+        crate::prefs::apply_new_design(app);
+    }
+}
+
 /// Before opening a file: a fresh tab unless the active design is blank. The empty design,
 /// new or already showing, takes Units of new designs so a cancelled open is not millimetres
 /// when the preference says otherwise.
@@ -455,7 +473,7 @@ pub fn tabs(app: &mut SolveApp, ui: &mut egui::Ui, r: Rect, x0: f32, x1: f32) {
     // A file loading into the window keeps the tabs as they are (dragging still moves it).
     let idle = !app.file_load.busy();
     if presp.on_hover_text("New Design (Ctrl+N)").clicked() && idle {
-        new_design(app);
+        new_tab(app);
     }
     match (shut, pick) {
         _ if !idle => {}
@@ -703,6 +721,21 @@ mod tests {
         assert!(active_is_blank(&a) && a.home.open);
     }
 
+    /// The tab strip's + opens a tab every time, an empty design's included; over the start
+    /// page's blank design (a launch) it uses that design.
+    #[test]
+    fn plus_opens_a_tab_every_time() {
+        let mut a = app();
+        a.home.open = true;
+        new_tab(&mut a);
+        assert_eq!(a.docs.count(), 1, "the launch's blank design is used");
+        assert!(!a.home.open);
+        new_tab(&mut a);
+        new_tab(&mut a);
+        assert_eq!(a.docs.count(), 3);
+        assert_eq!(a.docs.active, 2);
+    }
+
     /// Quitting asks once per design with unsaved changes: Don't Save moves on (and keeps no
     /// recovery copy), Save saves and moves on, and the app quits after the last answer.
     #[test]
diff --git a/crates/ui-egui/src/lib.rs b/crates/ui-egui/src/lib.rs
index ede551ac..8311be00 100644
--- a/crates/ui-egui/src/lib.rs
+++ b/crates/ui-egui/src/lib.rs
@@ -642,7 +642,7 @@ impl SolveApp {
                     // applying cancellation hooks (such as restoring its timeline marker).
                     self.dialog = None;
                     self.tool = None;
-                    self.preview = preview::PreviewState::default();
+                    self.preview.reset();
                     self.cam = Camera::default();
                     self.fit_view();
                 }
diff --git a/crates/ui-egui/src/preview.rs b/crates/ui-egui/src/preview.rs
index 25af7b69..f234ab8a 100644
--- a/crates/ui-egui/src/preview.rs
+++ b/crates/ui-egui/src/preview.rs
@@ -118,6 +118,15 @@ impl PreviewState {
         }
     }
 
+    /// Drop the preview of a design that leaves the window. Its scene goes too: the viewport
+    /// keeps drawing the last scene it took until the slot it reads hands it another, so a fresh
+    /// state (another slot, empty) would leave the old preview drawn over the next design.
+    pub fn reset(&mut self) {
+        let (slot, key) = (std::mem::take(&mut self.slot), self.key);
+        *self = PreviewState { slot, key, ..PreviewState::default() };
+        self.set_scene(GpuScene::default());
+    }
+
     fn set_scene(&mut self, sc: GpuScene) {
         if let Ok(mut slot) = self.slot.lock() {
             *slot = Some(sc);
@@ -1052,6 +1061,28 @@ mod tests {
         pv.poll(4, None);
         assert!(pv.error.is_none() && pv.shown_key == Some(1), "an old error is dropped");
     }
+
+    /// A design leaving the window (another tab) takes its preview off the viewport: an empty
+    /// scene in the slot the viewport reads, under a new key. A fresh slot left the fillet
+    /// preview of the old design drawn over the new tab's empty design.
+    #[test]
+    fn reset_hands_the_viewport_an_empty_scene() {
+        let mut pv = PreviewState::default();
+        let mut sc = GpuScene::default();
+        sc.xray_tri([0.0; 3], [0.0, 0.0, 1.0], [255; 4]);
+        pv.set_scene(sc);
+        pv.active = true;
+        pv.replaced = vec!["Body1".into()];
+        let slot = pv.slot.clone();
+        let key = pv.key;
+        // The viewport took the scene.
+        assert!(slot.lock().unwrap().take().is_some_and(|s| !s.xray.is_empty()));
+        pv.reset();
+        assert!(std::sync::Arc::ptr_eq(&slot, &pv.slot), "the slot the viewport reads");
+        assert_ne!(pv.key, key, "a new key: the viewport takes the slot again");
+        assert!(slot.lock().unwrap().as_ref().is_some_and(|s| s.xray.is_empty() && s.blocks.is_empty()));
+        assert!(!pv.active && pv.replaced.is_empty());
+    }
 }
 
 #[cfg(test)]