Windows 7 question

[brooksmoses]

Sometimes, when I hover my mouse cursor over the "Windows Explorer" tabs in the task bar, I get a nice pop-up menu of all the Explorer tabs I have open, with names and I can click on the appropriate one and so forth, and even close them from that menu. (This isn't just Explorer; it does it for any grouping of windows associated with the same program.)

Sometimes, instead, it just waits a few seconds and pops up a tooltip with the name of the one I'm hovering over, as if to mock me with how hard it's making it to find the right window from the five I have open.

Why is that? When it starts doing the latter, how do I make it do the former again?