I have also had this problem, although the symptoms are slightly different. When it happens to me any cell that I move to, or groups of are selected and I can't do anything else with the mouse in Excel, and even the keyboard seems to have no input. I also noticed on my laptop that other applications are affected although the problem is magnified in Excel. In other apps such as my web browser the mouse doesn't work at all for selection (left click) purposes. If I tap the scroll wheel and shake the mouse the issue may dissapear but does re-occur quickly. I believe the issue that I'm having is with the wireless mouse, and it seems to be when the batteries are just starting to drain. If I replace the batteries the problem seems to go away, although I haven't been consciously noticing if that's the case every time.
So I agree that it seems to be hardware related to wireless mice/keyboards. It may be driver related, or as in my case power related. I suggest trying to keep a log of circumstances when it happens to users - have they replaced the batteries, is it affecting the left click in other apps, do the arrow keys work on the keyboard, can they left click in Excel to save the file when it happens, and are the symptoms the same every time? I think in my case as the batteries get weaker, my symptoms do change. Anyway, good luck and I think you can get to the bottom of it by gathering as much information as possible and compare notes in all the cases. Does it happen at all on wired keybds/mice, etc.