Map: Dark Castle
Clearing out the surface level of the Dark Castle. Just killed all the skeletons, and caught sight of a pack of ghouls (on the northwest side) and dropped a flaming sphere on them, just as the scripted scene with Adam the Twelfth started.
I biffed the Persuasion check and got kicked out of the courtyard... and then the fight with the ghouls started.
Things got weird from here. I could misty step up to the walls and open the gate, but that changed Adam and his guards from passive to aggressive, but they didn't join the fight with the ghouls. Once all the ghouls were down, though, it immediately triggered combat with Adam and co.
In short -- don't let cutscenes run if a combat is pending.