'Error: process_creature_state: The creature IMP index 1126 has illegal state[1], S=0, TCS=0, reset'

This Error occurs frequently in the log nowadays. Introduced in Unofficial, no idea what triggers it.

Can be easily reproduced on any map with a computer player, for example level 5 or 15. Simply start the map, set frameskip to high, and afterwards check the log.