Gary, sir.
This happens ALL THE TIME. I know of at three circimstances, just in recent memory (past 10 years) in which people I know were effected by the FAA invalidating many checkrides conducted by either a DPE, or in the case of my students (in 2010), an FAA Inspector/Examiner who was unqualified to perform the checkride himself!!! True story. Sadly, this is an all too common occurrence in flight training.