We have a rare (but none-the-less, re-occuring) problem with Word (and sometimes Publisher, but nowhere near as often).
For some reason when working on Word, a user goes to click on the 'Save' button, nothing happens. Same goes for clicking on 'Save As ...'. Absolutely nothing happens. Clicking on the save to PDF/XPS button does, however, give the save dialog box, but only to save as PDF/XPS (as it should).
The fix for this is (so far), is to get the user to logout of the PC, then log back in. This is ok as long as the user has basic text, tables and pictures on the document, as the work can be copied out of Word and into Wordpad (it's just Word that has this problem, no other program does).
Unfortunately, due to the type of user account that is most used, we can't look at any system/reg settings because of restrictions, and logging the user out for one of us to log in fixes the problem anyway.
In a way this wouldn't be as bad if user's saved their work as soon as they create the documents ... but 90% of the time, the user has done "hours of work" only to find they cannot save.