Spire Complex - Map 9 Question

Hey all. I've been playing phobosdeimos1's "Spire Complex" WAD, and I cannot figure out how to get out of map 9. The boss is a ghost, and I can't kill him, so I can't exit it seems. Does anyone know why? Is this a bug? Or maybe I'm missing something? If anyone has any suggestions, I'd be glad to hear them! Thanks!

It's a known bug. If you managed to turn him into a ghost, you basically completed the map.

Ah, ok...I see. thanks!