Because almost all the zones have different ingame boundaries and the map is always in a static size then there is a need for a calculation based on the zone your currently in.
And because these zones arent supposed to be part of the game, these calculations were never included.
If you want to bypass this limitation and show the cursor in a wrong place you could always try to find the switch in the client and enable unknown zones.
The code is something like this:
CMP zone, 8
JE a
CMP zone, 12
JE b
RTN <- u could change this to a JMP a for an example