Hehe, that's actually not a bug. I did it for testing purposes.
Wrote in a way for Rotom to change formes now. There's a routine which you pass the slot ID in var 0x8004 (using the select Pokemon special), and the forme ID in var 0x8005 by setting it in the calling script.
It then calculates if the Pokemon is a Rotom, and if it is, changes its forme to the one you specified and recalculates the stats accordingly.
To change Rotom back to its normal forme, simply call its current forme again, and the code will revert it back to normal forme.