reading the logic here, it appears the routine dealing with otir sets memptr to bc+1
https://github.com/hoglet67/Z80Decoder/blob/master/src/em_z80.c#L2342-L2345

however according to visual z80 this is only the case when b == 0; otherwise memptr should contain the value PC+1 (arguably this is only observable when looking at a single intermediate state, rather than the state of when the loop returns to the calling z80 code).

i haven't actually been able to verify this is indeed what happens when running your code, as #1 prevents me from doing so.