Hanging Tooltips solved!
It appeared to be that an active button remained in that state when
another region/editor became active. It then kept the button-activate
state, and therefore also the optional tooltip.
This only happened on fast moves, when a mousemove event was not passed
on anymore to the previously active subwindow.
It has been solved with a new notifier (SWINACTIVE), which gets sent on
new active regions. The screen listener then calls uiFreeActiveButtons()
to find out if buttons were still active somewhere else.
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