Revaluation of On-hand inventory - PO Change

We recently had an IB type GL inventory entry that revalued our entire on-hand inventory for 1 part.  We do not know how this happened.  The item ledger was not affected and the frozen cost did not change.  In fact, we do not see this new unit cost in any cost version.  The only place this new unit cost appears is in a new PO that was created with a new supplier.  The entry created a journal entry for inventory revaluation, but did not revalue the item . . . throwing the inventory out of balance to the GL.  Any