>>I'm fairly certain I've seen it on things besides the 'X'. I think I've seen it on menu items. I need to pay more attention. It seems to be a bug, and it would be nice to have it fixed.
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>Any button in windows will have similar behaviour.. Sometimes it's a quick way to not press a button that you accidentally clicked on - If you slide teh pointer off the button before releasing the mouse button, the button will not actually click. I've noticed this behaviour since way way back...
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>Jonathan Chan

A well appreciated feature for people like me having second thoughts about a "click" :-)