excel skips to another workbook for no apparent reason

I believe I diagnosed the root of this problem. But I have not necessarily determined a "fun" solution. The issue has something to do with the automatic movement of the active cell upon clicking enter. Excel lets enter move to the right, or down or other such things. There is some sort of glitch or special situation that moves the cell to a different cell in a different open workbook instead of the one you are currently in.

I have solved the problem by going into Options_Advanced and unclicking the "After pressing enter, move selection" setting.

It is a little odd because I used enter to move around the spreadsheets and I am having to adjust my behavior. But the random pop up spreadsheet issue is gone.

I believe I diagnosed the root of this problem. But I have not necessarily determined a "fun" solution. The issue has something to do with the automatic movement of the active cell upon clicking enter. Excel lets enter move to the right, or down or other such things. There is some sort of glitch or special situation that moves the cell to a different cell in a different open workbook instead of the one you are currently in.

I have solved the problem by going into Options_Advanced and unclicking the "After pressing enter, move selection" setting.

It is a little odd because I used enter to move around the spreadsheets and I am having to adjust my behavior. But the random pop up spreadsheet issue is gone.

Glad this helps KyleL630, but no; this cannot be a root or proximal cause.  I have always had moving selection after pressing enter turned off.  (I hate that default whenever I use someone else's computer because I spend a lot more time editing equations than data entry.)

Well I appreciate your comment. Although it was a little presumptuous to think that this was incorrect, it merely did not tell the entire story. This did indeed stop the issue from happening to me. But why it did turned out to be a secondary behavior issue. I was able to force the issue to occur about 50% of the time in a specific scenario after a couple of days of no issues. You were correct that the timing has to do with typing in the formula bar. I do a lot of typing in formula bars and that is when the issue occurs. I was able to duplicate the issue whenever the cursor was in the center of a formula and I clicked enter (about half the time). Since I was using the enter to navigate to the next cell I would do this often to be done typing and to be at the next cell. So by using different methods to confirm the formula and by keeping the cursor at the end of the equation I have not had the problem duplicate. I cannot say for sure if there are other ways to make this occur, but it was the first time that I was able to repeat an action and see the problem after the action. 100%, nope, but about half the time. I was unable to get it to occur when the cursor was at the end of the formula.

For anyone interested, I've posted a workaround and my findings on page 8 (https://answers.microsoft.com/en-us/msoffice/forum/all/excel-skips-to-another-workbook-for-no-apparent/272ccfbf-5aca-43f4-8e8f-c55a38043a0e?page=8)

TLDR: Follow the steps on this link: https://support.microsoft.com/en-us/help/3165211/how-to-force-excel-to-open-in-a-new-instance-by-default

Awesome good find! Thank you for posting that alternative workaround to automate it.