excel skips to another workbook for no apparent reason

I have the exact same problem, for about 3 years as well.  This happens several times a day and is beyond frustrating--I am hoping that if enough people complain, they will do something to fix this--

I will also try opening the spreadsheets differently, but it is cumbersome and I know I won't always remember--

I'm glad I read this, as I was just about to buy a new keyboard, thinking there was a shortcut or hotkey programmed that I didn't know about, or set on accident.  I can't find a way to identity assigned hot keys, either, on a separate note.  That's how frustrating this is--I'm resorting to buying new hardware in hopes of eliminating this problem.

We haven't seen any issues at all. Everything works the way it used to.

If you have problems, just clear the setting. It's a single switch being turned on or off.

Thank you.  I will give the registry change a shot.  I was a bit leery to do so, since someone mentioned that it creates issues with cutting/copying/pasting, which is a big issue for me, but I will see how it works out.

Yes, this is precisely the set of symptoms we see as well. Sorry this wasn't pointed out. However we have found that registry change forcing single instances has eliminated the problem. It has not recurred, and we don't find significant other problems as a result. There do seem to be some other strange Excel weirdnesses, but I do suggest you try the registry change.

Spot on.  Microsoft, are you listening?