Flitwick as DADA professor?

[justcarol67]

No: HPFGUIDX 90873

I was rereading OoP last night and realized that the teacher giving
the DADA exam to Severus and MWPP in "Snape's Worst Memory" was
Professor Flitwick! If he was the DADA professor twenty-one years
earlier, why is he teaching Charms now? Granted, he seems much more
suited to teach Charms than DADA, but still, why the annual search for
a DADA professor (setting aside the possibility that Snape could teach
it) when Flitwick is still available? Why not give the position back
to Flitwick and find another qualified Charms teacher? That would
almost certainly be easier than finding a good DADA teacher (other
than Lupin), which seems to be nearly impossible.

The only explanation I can think of is that something happened to the
real DADA teacher during Severus' fifth year and Flitwick was filling
in for him or her during OWLs--rather like Professor Grubbly-Plank
filling in for Hagrid. (Really, she ought to be given the job
permanently, but that's a topic for another post.)

Ideas, anybody?

Carol