Hmm I'm not really sure what could cause that. Maybe a corrupt file triggering... or something try reinstalling or something because I know some people have troubles with dungeons and others don't. Like I dc at the Underground Monastery when I click "Sing the song". But there's the alt tab way etc. so maybe there is a simple solution for it somewhere try googling or something, also try improvising like alt-tabbing just before 15 minutes you know or pull boss away from that spot and kill him at the altar xD you know what I mean. But thats the best I can think about atm.
EDIT : Also is this with hacks on or off?
EDITEDIT : Does this happen in A/B/C ? If it's C try see'ing if it happens in B. Don't even try A you won't find a run for it ^^