This question already has an answer here:
I wanted to reply to the following thread: taskbar icon preview (and Alt+Tab icon preview) disappears quickly
But I am not allowed to. So I am created another here to share my experience.
First, the Behaviour
When you move over the application icon on the taskbar (that has application opened), you would expect a preview to appear. In this case, although the preview window appears, it will simply auto-disappear (i.e. closed by itself within a very short period of time, e.g. 1s). This behaviour is also evident when you use Alt-Tab.
Editing the registry, etc, does not help for me. Setting the aero peek (enable or disable or a mixture of those) also does not help.