[Retros] DR vs forced ep: what rule predominates?

[Joost de Heer]

I just remembered that something like this already exists:

8068 - Alexander Kukush
Feenschach 135
4kb1r/4ppp1/4Q3/6P1/4PK2/8/6P1/8
5+6. Mate in 1 (AP, PRA)

Black tries to castle, thus proving it's possible that he didn't move 
last. But: 1. .. fe6 2. g6 e5 3. Kg5 e6 4. g4!! and now is 4. .. Be7 
mate, and other bishop moves result in stalemate. So black can't prove 
he didn't move last. So mate in 1 with 1. Qc8#.

Joost