For what it's worth, I've had trouble with plastic explosives in the Vault City courtyard as well (although I must stress this was the unofficial patch, most recent version, and not the RP, so it may or may not still apply). The explosions weren't triggering where the bombs were dropped sometimes (even if they were planted on someone), instead often choosing this one particular spot in the corner of the fenced-in servant area, or occurring offscreen. I'm pretty sure it crashed the game at some point as well, although I'm not sure that was in the same area. Oh, and when they occurred offscreen, the bomb on the ground... didn't go away. The description still said the timer was ticking, so it probably left a useless non-exploding-yet-ticking plastic explosive behind.