Release the Slice Button's Mouse Capture When a Press Loses Its Release

src/slic3r/GUI/Widgets/SideButton.cpp

@@ -17,6 +17,7 @@
 BEGIN_EVENT_TABLE(SideButton, wxWindow)
 EVT_LEFT_DOWN(SideButton::mouseDown)
 EVT_LEFT_UP(SideButton::mouseReleased)
+EVT_MOUSE_CAPTURE_LOST(SideButton::mouseCaptureLost)
 EVT_PAINT(SideButton::paintEvent)
 END_EVENT_TABLE()
 
@@ -331,20 +332,30 @@ void SideButton::mouseDown(wxMouseEvent& event)
     event.Skip();
     pressedDown = true;
     SetFocus();
-    CaptureMouse();
+    // Capturing twice pushes this button onto the capture stack twice, and the
+    // release would then hand the capture straight back to it.
+    if (!HasCapture())
+        CaptureMouse();
 }
 
 void SideButton::mouseReleased(wxMouseEvent& event)
 {
     event.Skip();
+    // A press whose release went elsewhere still holds the capture.
+    if (HasCapture())
+        ReleaseMouse();
     if (pressedDown) {
         pressedDown = false;
-        ReleaseMouse();
         if (wxRect({0, 0}, GetSize()).Contains(event.GetPosition()))
             sendButtonEvent();
     }
 }
 
+void SideButton::mouseCaptureLost(wxMouseCaptureLostEvent&)
+{
+    pressedDown = false;
+}
+
 void SideButton::sendButtonEvent()
 {
     wxCommandEvent event(wxEVT_COMMAND_BUTTON_CLICKED, GetId());

src/slic3r/GUI/Widgets/SideButton.hpp

@@ -94,6 +94,7 @@ private:
 
     void mouseDown(wxMouseEvent& event);
     void mouseReleased(wxMouseEvent& event);
+    void mouseCaptureLost(wxMouseCaptureLostEvent& event);
 
     void sendButtonEvent();