More a query than a problem:
I used to be able to boot the ROM disk in my Macintosh Classic with the usual CMND+OPT+X+O key combo on boot. Now, strangely, this key combo only sort of works. Instead of booting into System 6, it will boot off the HDD into System 7, but the 'Boot Disk' will appear on the desktop! Sometimes I can open this, other times it comes up with a 127 error.
If I do manage to open the ROM Disk and use the Startup Selector to select the ROM Disk, I can boot into the ROM Disk without using the key combination.
I have a Mac Classic too and what you describe is normal on mine except for the 127 error. My Mac won't boot that ROM disk unless the internal drive is absent, or I select the ROM disk in the Startup Disk CDEV.
Glad it's not just me then. Wonder why it used to boot into the System 6 ROM and now it no longer does (unless you use the Startup Disk selector). The only thing I have changed is I wiped the hard drive and went from System 7.0.1 to System 7.1......
For posterity, resetting the PRAM with Cmd-Opt-P-R fixed this right up.