Word does not close properly, which creates locking in NAV

After using Word to edit Sales Quotes, Word does not close properly, and this leads to locking errors in NAV.

Our client uses NAV 2016 (build 45834), with Remote Desktop Web access. The RD Web server is Win 2012 R2 Standard, and this is separate from the NAV server and the SQL server.

Users open the NAV client through RD Web access; they then use the “Open Document” feature in NAV to launch Word.
The problem only happens if Word is closed from the “X” button. If Word is closed by going to File – Close, there is no problem.

Have you ever encountered this? Do you know if there is a fix to get the "X" button to work the same a "File - Close"?

Thanks
Alastair