From the todo:

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.

source/blender/editors/include/UI_interface.h

@@ -322,6 +322,7 @@ void uiBlockSetEmboss(uiBlock *block, char dt);
 void uiFreeBlock(const struct bContext *C, uiBlock *block);
 void uiFreeBlocks(const struct bContext *C, struct ListBase *lb);
 void uiFreeInactiveBlocks(const struct bContext *C, struct ListBase *lb);
+void uiFreeActiveButtons(const struct bContext *C, struct bScreen *screen);
 
 void uiBlockSetRegion(uiBlock *block, struct ARegion *region);