Powell was never as much in power as he wanted to be which is his reasoning for all the stupid comments he makes. He's mad because the President didn't really trust him.
I don't actually think it had to do with trust as much as it had to do with Powell following the President and not vice versa.
I believe Powell was under the impression that he was going to RUN the state dept by making POLICY decisions .. and he was caught several times making decisions which were not sanctioned by the WH. Powell then had to apologize to the public and make a statement to that effect. I don't think he much appreciated Bush making an example of him. He resorted to saying - I serve at the President's pleasure .. but I don't think Powell ever got over it.
To add to the fray .. Armitage was on Powell's side against Cheney and Rummy. And .. I don't think he was exactly helpful in smoothing over the Bush/Powell dustups.
But .. I never liked the choice of Powell from the beginning so none of what he did was much of a surprise to me.