Thanks for all the information. That colon was easy enough to edit with a hex editor (essentially moving the string over by one char and making the former end of the string a \0.)
I have also made a pull request
about this but thus far it has not been accepted yet (and their auto checking routine seems to be doing something strange as it said it "failed all checks" even though all I changed was removing the colon from a string.)
I'll also look into recompiling mame too once I get around to setting up the build environment for that.