Sir, I have an idea on the matter regarding the whole incident and I'd like to hear your perspective.

The castle here is pretty old right? And it's been exposed to a pretty high concentration of magic and has been imbued with tons of spells throughout all of those years correct?

Wouldn't it be plausible then that due to all that exposure over the years that the castle has a kind of magic of it's own kind and sometimes it acts on it's own volition? And that this incident is a result of that?