If you open the Monitor in the first example and step through it in the debugger, the byte at address 0xFE changes at every step. This doesn't seem to be documented and it's not clear to me why it's doing that.

Moreover the content of 0xFE keeps changing even after execution stops (if you keep hitting the "step" button).

0xFF isn't even listed, but a load from that address seems to work (with value 0x00). [ETA: actually, that seems to be a quirk of the Monitor's initial config. If you set "length" to 100 instead of ff, you can see byte 0xFF in the monitor. Nothing wrong or weird there.]