Yea, there's a bug, I just discovered you can "upgrade" a medical depot to a lvl3 sentry gun "model". It's just a model, not an actual weapon. It's fixed, but it was a weird bug and you had to hammer the upgrade command while on top of it...
Score one for the bots.
There's nothing for the mappers to do with this, the AI will adapt depending on the map. I'm using a new build of BSPC.