The interesting question is what should happen on a warm Select+Reset. Looking at the documentation again, it implies that it might just trigger a cold reset instead of bringing up the menu. The thing is, cold vs. warm reset isn't determined by the hardware on XL/XE machines, it's determined by the OS. I don't think interrupting a warm start is enough to force a cold start, so it'd have to either involve assistance from the menu OS or injecting instructions to clear the warmstart state from a hidden ROM.
Correct, Select+Reset triggers a cold reset, but only with the APE Warp+ OS. Other selected OS's do not do this. So its not a function of the hardware, but the selected OS.
The behaviour of the "OMNIMON TEST" OS is that it will boot to a blank screen if BASIC is disabled with OPTION pressed... So emulation the emulation is accurate. It will boot to BASIC if it is enabled. From there a 'BYE' does absolutely nothing - you can then enter more BASIC commands. Probably just jumps to an RTS. Select+Reset at this point will get you into "OMNIMON XL © 1984"