assuming the traitors are not communicating with each other directly via PM
You missed an important point in all of this (including your faulty assumption, but I think it stands for itself). Even if there was no communication via PM, it still could have gone down like this:
It was game 3 when the two traitors, Mack and Crow, were on the same team. Mack had just struck last round, so he was a pretty hot target. The terrorists had the game tied at 1-1, which puts the terrorists at a huge advantage. There was no need to push this though, so one of them let the operation succeed. Probably Mack. Crow, not knowing who is cohort was and being a little distracted, does the natural thing and fails the mission.
This makes the situation better than Mack would have expected! Not only does it fail a mission, putting the terrorists on the up-and-up, but they only suspect one terrorist from among the group.
This is just as plausible as your theory. You are overthinking it.
Mack and Crow have probably been in communication, thus mrxak's big "I am looking into this" post. Honestly, I don't blame them for using communication; if I were a terrorist, I would want a leg up on an op containing both terrorists.
All of this to say, this vote needs to pass or else Mackilroy (the next proposer) will substitute my name for his; the motion will probably pass, and it'll be failure for the innocents.