(This happend on a clan server. This may be allready fixed and that server is/was using an older QVM)
When as an alien, it is possible to kill human structures. However, if the explosion of the buildable explodes and kills an alien buildable, it will say that that buildable was Teamkilled by the person who blew up the human structure. Because of this, I would infer that if you make a builable blow up and that kills a teammate, you will get a TK on your tremstats (remember me?) record.
The other glitch was on the official servers. I recall being on the alien team in niveus when a human dropped the grenade on top of the lowered door. When the door went up, the grenade went halfway up with it and starting jumping really fast and spamming the bounce noise. Because it was higher off the ground, it was able to reach the non-nadeable structures and a granger.
There was another bug but I don't remember it off the top of my head.