This one is going to join the well worn aviation sleeping dogs list:
Night flight in the UK on an FAA PPL (without an IR)
FAA medical for a piggyback FAA PPL (with an IR)
Can't think of any more off hand...
These are never likely to be settled.
That's before one gets onto stuff which is a grey area even
within the USA, like whether a "flight" with 3 landings needs to be done on the same day.....