Don't have a save, unfortunately. A Greater Doppelganger/Kiel in the same room as above spawned when I slept. The party damaged it until it came up as 'Dead', but it was very much alive still and attacking the party. Continued damage had no effect on it. I eventually re-loaded to avoid the problem.
// Log of Currently Installed WeiDU Mods // The top of the file is the 'oldest' mod // ~TP2_File~ #language_number #component_number // [Subcomponent Name -> ] Component Name [ : Version] ~SETUP-BGT.TP2~ #0 #0 // Baldur's Gate Trilogy - Core: 1.08 (19 Oct 09) ~WIDESCREEN/WIDESCREEN.TP2~ #0 #0 // Widescreen Mod: Widescreen Mod v2.2 ~SETUP-BGTMUSIC.TP2~ #0 #0 // Baldur's Gate Trilogy - Music -> Full Baldur's Gate and Tales of the Sword Coast Music