Another thing I've noticed is occasional sluggishness in the UI. It's hard to pinpoint, I often feel like my clicks are being lost.
For me some clicks are counted double (or wrong).
From the welcome-workspace hightlight MetacelloConfigurationBrowser open.
and use the Mouse and context-menu for "do it". It opens the configuration browser, but
it reopens the menu as well. The same happens for other mouse interactions as well. Open a Browser. Click on the codepane, open context menu, use left-mouse button in another browser pane -> the context menu closes and reopens again at the new mouse position.