John Clonts wrote:

snip
Later I thought that maybe the tower didn't realize I was IFR when he
cleared me for takeoff, and that fouled something up with departure.
snip

This is an interesting thread. I'm based at a class C, RDU, Raleigh-Durham, NC,
and I've never had that happen, and I've never informed tower that I was IFR.
Never heard anyone else do it either.