I know it's from a mod and not from the original game, but during the quest "Kidnapping of Boo" from "Unfinished Business", Minsc is affected by two spells: wwnoboo.spl and wwboo.spl. They respectively happen when Boo is stolen then when Boo is given back to Minsc. Some of their effects that I know from Near Infinity don't work. As the second one is basicaly the reversed version of the first, I will only describe the second.
First, this spell use "Change portrait" on Minsc (large NMINSCM.BMP, then small NMINSCS.BMP) but the result is that the small portrait is correctly set and well displayed, but when entering the Minsc's character window, GemRB looks for NMINSCSM.BMP, logicaly fails to find then load a question mark picture instead. (last test before posting! Changing the order of these effects solves the problem but that's not really a fix)
The second effect that doesn't work is the "Create item in slot"... No item is given (and I guess that Boo is forever lost...).