Why is the Autosentry destroyable by teamates

Ive had quite a few people wonder over to my sentry, wonder wtf it is, and then melee it out the air lol. Shouldnt this be fixed?

Was there Friendly fire in that game type? If so then thats why they can break it, if not well then it would be a bug.

Nope, no friendly fire. I was messing around with my mate actually trying to kill him for the sniper rifle and couldnt haha.