I found the problem (and a temporary workaround). There was no file corruption on my system as I first suspected! The culprit is the "lsaveposition" property of the form. I changed this back to .F., deleted the associated key in the Windows Registry, and everyone is happy again.

In my confused mental state at the moment I am uncertain if this problem appears in forms based on anything above cBizObjMaintenanceForm in the class hierarchy (I don't think so).