Trouble shooting: excel file not saving while giving no error

I have users (more than one) saying that they are trying to save excel files and swear they selected save and it gave no indication that that save had failed.

However when they go back to it later it is the old version, so clearly they had not saved it.

This is apparently not a constant issue - just once in a while and I haven't heard of it occurring with other files but since they are heavy excel users that may not say much.

This is computers running excel 2010 on windows 2012 via Remote desktop (if that helps).

Are there any known issues I should be on the look out for? Or is the problem more likely to be in the chair as opposed to on the desk? Or beyond the scope of this forum?

I thought this sort of thing would be next to impossible, so any hint would be useful.

Just a thought but are these files common to many users?

If so and assuming it's not been set as a 'Shared Workbook', could it be that the file has already been opened by a user which would mean that any changes made by others when they too open the file at the same time will not be saved unless they choose to save the file with a different name.

OK I will look into if they are using shared files and if others might have been in those files at the time.
Might take a little while as the communication isn't direct.