The issue probably has to do with resource (fork?) compression/decompression. This feature was (for no good reason?) removed in 9.1. There's quite a list of software that got affected by this, such as After Dark, and possibly also Power MachTen, although the former got a patch fix for it, and the latter even an official patch fix.
If you can bring this ability back to 9.1, and thus also 9.2, 9.2.1, and 9.2.2, it might fix the problem entirely, and also fix a bunch of other software.
I don't think it has anything to do with the "ROM" file: if you install Mac OS 9.2.2 on an Old World ROM machine (using i.e. OS9Helper), you will most likely encounter the exact same issues.
Also, when you ask for "version 9.1 of the ROM", do you mean a ROM file included with some release of Mac OS 9.1, or a ROM file whose version is "9.1"?