This ones been messing with me for awhile. Do you remember if you killed the boss in bat form or vampire form? Any other details you can recall about how he was killed?
met the same bug, I have tried this twice (by reload the game), in bat form you will trapped, but in normal form the door will open. btw, I counter two more bugs, 1. the dash attack seems not work for me, 2. in some case the when entering last level of the core the game would stuck.
