Finished up and found two more things going wrong in MAP30:
First, at least in Doom 2's map 30, if you talk to the one and only enemy and try to get his quest too quickly, GZDoom freezes and needs to be end-task'd. I think the point at which your are safe is when the first cube lands and spawns a demon; merely waking the boss brain isn't enough.
Second, if you pick up and throw the Wacky Wizard around somewhere before talking to the Wizard, this happens.
