@sy2002 @MJoergen I have opened an issue on the Mister C64 core github related to the "frREUd" REU demo which fails on the Mister C64 core and of Course our own c64 core :
MiSTer-devel/C64_MiSTer#186
I have asked gyurco (who is maintaining the c64 core on MIST) to check if the demo also fails on MIST.
interestingly, it doesn't fail on MIST.
I'm waiting for sorgelid answer, but i thought that, in the meantime, it could be interesting to check what differs between both REU implementations.
The MIST c64 core is hosted here : https://github.com/mist-devel/c64
So, if by chance, when both of you have some time maybe you can try to figure out what's the difference between both.
I will check if/when i get a feedback from sorgelid.