Quote Originally Posted by drone View Post
I'm pretty sure you take a influence hit from this. Never lost a crusade this way myself, but I did cause the French the rebel when I backdoored the Chapterhouse of a crusade coming my way. Not my fault he left the province lightly defended...
Destroying your own chapter house while a crusade was active was an old "cheat" for triggering a civil war. Destroying it yourself has exactly the same effect as it being destroyed by an enemy incursion (actually losing the province/battle is also a factor in loss of influence however).