This started about a month or so ago. I don't remember changing or installing anything around that time, though.
Basically, my taskbar icons don't behave correctly. After I click anywhere on the taskbar, the taskbar acts like I never remove my cursor from the taskbar. Like icons keep that 'glow' on them as though my cursor were over them, and then they pop up a tooltip with the name of the window, or an unopened program's icon gets those little lines to the sides and the glowy bit at the edge as though I were hovering my mouse over it.
Here's a screenshot (I drew in the approximate location of my cursor at the time)
Furthermore, when this is happening, I can't hover over taskbar icons to get the window previews. It just shows a tooltip with the window name, or nothing if it's a group of icons. As far as I can tell my Aero settings are all fine, and I know I haven't changed them in at least a year. Here they are anyway:
The only way I can fix this is if I drag an icon so it displays the jumplist. Right-clicking to display the jumplist does not fix it. Only dragging does. Then all's well until the next time I launch via the taskbar. I can hover for window previews, there isn't a glow when there shouldn't be one, etc.