I discovered what it seems like a bug in chd support for the beetle saturn core. Last Bronx, in either PAL or USA versions, does not work when loading in CHD format. The systems loads the bios fine, and then the screen shows a corrupted screen and nothing else. Strangely, this does not happen with Japanese version, but both with Pal and Usa versions of the game. Game works fine when in cue/bin format.
If you take the compressed chd and uncompress it back to cue/bin using exctractcd chdman command, the resulting uncompressed image works ok. So the problem must be on the chd support on beetle saturn core or retroarch itself, it’s not a problem with the chd standard.
Of course I tried with different source images and with redump verifies dumps. I’m using Retroarch 1.7.2 and chdman 0.197, and using the md5 matching bioses for the system.
I’m not complaining, it’s not a problem for me to use the uncompressed image, but thought I could report this bug so someone can take care of it.