> You cannot apply the source to the MAME release source, you have to pull from github
> to the tag. Back then tags had random names, you'll need to look at the list of them.
> I don't know the specific git commands. Also, tags have not always been in use and it
> won't be easy to try making an old build.
I assume by "tag" you mean the hash value of the commit. I've done that for the HBMAME github repo, using tag values for "good" and "bad" builds as the git bisect command requires it. Regardless, it sounds like it would be too difficult to attempt a git bisect.
So for reference/convenience, here is the scenario of things that work and don't work. I'm happy as always to help you troubleshoot and fix this bug.
$ hbmame -rompath /mnt/shoegazer/roms monaco
$ hbmame -rompath /home/shoegazer/roms monaco
$ hbmame -samplepath /mnt/shoegazer/samples monaco
$ mame64 -rompath /mnt/shoegazer/roms pacman
UPDATE: I compiled a new HBMAME from a post-0.186 git snapshot and it's working again. I assume it was due to a bug in MAME somewhere between 0.184 and 0.186 affecting ROM paths.