RPi4 USB Boot Drives (?)

I may have discovered a flaw with the way USB boot drives are handled with ROM 11/10/20.

I recently swapped my over my USB HD4 drive 0 from my Pi3 to an 8Gb RPi4 without issue. However on inserting another USB HD4 drive 0 from the 8Gb machine, it showed up as expected as USB Device 2. Clicking to open it, it switched !Boot to that drive, closing the other !Boot drive window. You click on either drive 0 or 2 and it switches !Boot drives. I know from my RISC OS 4 days that when I’ve swapped over a hard disc with another !Boot sequence visible at root, the original is locked to the drive it started from. This doesn’t appear to be the case with a USB drive on the Pi4. Perhaps, I was unlucky, but it was something that I observed.

Your drive are using the same volume name, rename one the drives.