I was working for T'rang and headed over to Umpani Fort to look for the Missing T'Rang Z'Ant mentioned. While there I did "the double agent" thing and did a few Umpani quest (ie got to the point where I got the level 3 security pass. I then went back to T'Rang base and Z'Ant accuses me of betrayal and T'Rang go hostile
It seems you can only do a few of the beginning quests as double agent before one can turn on you.
But thanks for the input about the Blunder Buss, that is definitely a plus !!