Sharepoint not saving changes made to Word documents

Opening a file in Sharepoint from Internet Explorer in Microsoft Word allows the user to (subject to permissions) make amendments to the file and use the save button to save straight back to the Sharepoint repository.  

However in certain circumstances users may make changes however not see those changes replicated in Sharepoint (despite no errors being displayed).

One main indicator that Sharepoint and Word aren't playing nice is that when editing the document the green "sync" arrows aren't displayed (see icon above).  The one cause of this I have encountered is where users are using the 64 bit edition of Internet Explorer, it seems to be related to the support within 64bit IE of ActiveX controls.

The solution is don't use the 64 bit edition of Internet Explorer, however users ma have been making changes oblivious to the fact that they aren't being saved.