Empire units placed in an Empire Prison in the map editor don't become imprisoned after capturing it
I consider doing such a thing a map design error, because it makes no sense for the Empire to do that to its fighters, it should be disallowed. There are two parts of the bug:
- Such units are never made prisoners by the game, as indicated by their activities such as "Going to Lair".
- Hence, after converting such a Prison they do not become your prisoners. You can harm them with Thunderbolt, for example, but their corpse/unconscious body will not appear outside of the prison. Your units will not consider them valid targets for attack though.