This file is in use error received with build 14701-20248. Cannot link multiple users to same back-end

One of my clients updated to build 14701-20248 and is no longer able to access the back-end in a multi-user environment. Those still on build 14701-20226 in his office are able to operate as usual. Full message received is "This file is in use. Enter a new name or close the file that's open in another program." Luckily only two workstations were updated. Does Microsoft have a workaround or is a fix in the works for this issue? I suspect it's related to the lock file not being released when a front-end or back-end is closed (reported elsewhere), but this is far more serious since this database is used in a manufacturing production environment and they need multi-user access to the back-end. Suggestions? All the typical solutions were tried (new front-end, copy back-end tables to new database, compact/repair, etc.) before realizing it was a version issue.