This happened to me starting in 2013 (through Office 365) as well. It was infrequent enough that I dismissed it, and never heard anyone else have that problem.
Upgraded to 2016 around March/April, and it still happens. It seems to be getting worse.
Today I am going through a list of dates and some of the dates have the wrong year. I edit the cell, just changing 1/1/2013, backspace the 3 out, add 4, press enter. Do the same to the next date, and pressing enter, and the keyboard is non-responsive as
has been explained before. I hit enter again, and it moves to another spreadsheet I have open.
This happened a few times in a row, this is the first time it was repeatable so I tried it again slowly. I always thought maybe there's some keyboard shortcut I must be hitting. But no, deliberately pressing each key I can confirm I am not pushing two
keys at the same time.
I decided to google again since it's been months since I looked, after trying a few different phrases and wading through a lot of vba macro results (no macros on any of the open spreadsheets), I am glad I found this thread, and wanted to contribute to it.
This happens both on my work computer (win 7) and home computer (win 10 free upgrade), and also found one other person at work with the same issue.
Edit/Update: After I posted above, I went back to edit more dates, and it still happened. (note I forgot to mention it would always switch to the same spreadsheet, though I had 4 spreadsheets in total open). I tried the only suggestion, to not have the
other windows maximized (I pressed the resize button to un-maximize the window)...I tried it with just the spreadsheet it would always switch to, and it didn't work, it still switched to the now smaller window. I then tried resizing and minimizing all 3 of
the other spreadsheets, it did switch once but then it appeared to stop happening. I re-maximized all the worksheets and so far it seems ok. I hope this gets fixed permanently but next time I'm in this situation I'll try it again and post here.