If you sided with dawnguard and you go home and talk to your spouse, if the quest Rescue starts load your last auto save and talk to that Arkay guy (I for get his name Fin-something). If you don't you the quest arrow will point to kill a vampire that doesn't exist locking you out of the ability to get dawnguard rune gear you didn't get yet.

Never encountered this glitch, sorry.

Currently experiencing this now, do we know of any fixes yet?