Two small issues while working in the designer mode:
1. Try to to rename a widget to a name that already exists(happens to me occasionally). An error dialog will be shown. After that try to create any widget(by dragging it from the widget-panel) - it will follow to another error: "Exception during creation of ...."
2. It occures while dragging any widget to a grid cell. Grid should be at the bottom of the screen, so that you have to scroll the window to see it. As far as i can tell, scroll-offset isn't taken into calculation of mouse position and wrong cell is highlighted.