The hover "feature" does this: when you hover the cursor over something for some period of time, the system assumes you want to click on it, and does. You did not click, but you hovered for long enough for Win7 to think you must have wanted to. It assumes a purpose to your pausing where none may exist. You may have just paused to, say, read something, decide something, or think about something... and your computer charges on, taking that pause as a signal to go, go, go.
Imagine if life worked that way. Careful what you stare at. Keep your eyes moving. Always moving.
It's another example of the system "outsmarting" you in a possibly stupid way. Win7 is just trying to be helpful, but it makes a click decision FOR you that you may not intend. Saving you all the bother of actually clicking, I guess.