I just uploaded a fix attempt. It seems like switching form into thief does not cause it with this new fix. At least with my local testing... Not 100% confident though as this bug has been rather stubborn and slippery for a while now.
Created an account just to give you a bit more info on this bug i encountered it twice and both times it happened when a level transition happened while wall jumping with the theif.
it also must be saved in the code somewhere cause when it happens it completley screws that save file if you save after it happens. cause of this i have lost 20 mins of progress so i hope this info helps eleminate the bug