I have no idea why, but a bit more info might help others figure this out:
What Operating system?
Are the spreadsheets inserted as a file or an object? (Objects are a Windows only option here)
How are you opening them, by double clicking or using export field contents?
Right click to open worksheet.
Are the spreadsheets inserted as a file or an object?
If you try this on another machine, do you get the same issue?
I discovered the root of the problem. I installed a timer script to comit after 60 seconds after keystroke in the layout script trigger. I did this because people would keep FM open on a particular field then throw in down in the doc. I was unable to work on the databse when their page was still open and according to FM working. Was comit the wrong script to use. What trigger could I use so that they could work in Excel out of FM and I can work on the database as a whole?
If "work on the database as a whole" means that you are making changes to the design of your database, you shouldn't do that while others are using it. This can create problems for them as well as you. It can also lead to a damaged database file.
If you are just doing data entry in other parts of the database, I don't see why another user working in an excel file would lock you out of making data edits in FileMaker.
To repeat my earlier question. How is the file inserted? As a file or an Object? How are you opening the inserted file? (there is more than one user action.)
Don't really see how commiting a record in FileMaker closes an Excel file, so would like to replicate your exact steps here...