We got suffer from this issue at least for times:
Each time there was no mappings on Number (apart from initial mapping) and some mapping (to Part Number) apper after.
I've already opened two cases 07963904 and 08572009.
First one was closed because we refused to provide full database (IMHO in this case it is unnecessary).
Second was closed as confirmed and fixed.
Yet issue keep happening...
Should I mention that it become quite annoing for me now?
I've seen this as well. In fact, I've noticed that mappings will automatically appear on 4 properties related to items; Number, Title, Description and Equivalence Value. I believe the trigger for the property mappings to suddenly appear is vault migration (e.g. adding a SP or hotfix, restoring a backup). I personally have seen this occur a few times when taking a VP2013 backup and restoring it.
Therefore, best advice is just to look at the existing mappings for the properties above and then after the migration go in and remove/change the mappings that appeared but are not right.
-Ryan
Ryan Small
SolidCAD