file may have been changed - copy or overwrite

We have office installed in a terminal services
environment. When documents are opened using the network
supplied Excel application, the following message always
pops up when save is clicked:

The file may have been changed by another user since you
last saved it. In that case, what you you want to do?

This happens even though the workbook is not shared and is
opened from an unshared directory. Is there a way to turn
this off?