, AndyC wrote

*snip*

Yes, that is the concern. And the absolute most ridiculous way to try and prevent it is to have that button be hidden until you mouse over where it is, because then you're almost certainly going to have the situation where someone moves the pointer over what looks like the switch target and has already clicked the button before realising the magic close button has suddenly appeared beneath their cursor and they've just quit the application they wanted to use.

It doesn't seem to have caused much of a problem with Windows 7's taskbar thumbnails, which show a close button when you hover over the tile.