The bug seems to be that when I play a Titan, then play another weapon over it, the Crusader not only endows the current weapons skill, but gets momentum as well. If the Titan gets destroyed, stolen or animated first, naturally it doesn't happen. Reproduced in trainer.
Edit: I noticed that its not really the problem with Endow as a problem of weapon slot. If I play Titan, then another weapon over it, the weapon hits through shields