If you are in Ed's Room Before the Doorbell rings, the cutscene will change from the one where Ed interrogates you after catching you, to the one where he's excited because the doorbell rang. You will be left in his room, and if you try to interact with the room or leave, ScummVM will crash with "ERROR: (26:89:0xF) Invalid actor 255 in o2_putActorInRoom.
I used Linux (Ubuntu x86 32-bit) 1.3.0svn52786.
In Ed's Room Before the Doorbell
My Maniac Mansion version was NES/English (US).
Kirben, could you please take a look?
This is a duplicate of bug #1447058, which I fixed in December 2010 for the PC version. Using the savegame attached here, I just verified that my fix from then also applies to the NES version.