Possible Crackdown co-op achievement problems

If you've been playing Crackdown co-op style, then we need your input. After playing co-op with a friend the last two nights we noticed a problem with the achievements in the game. The problem arose when I was invited to a co-op Crackdown session, which was easy enough. Hours went by, we were leveling up our characters, earning achievements for such deeds, and even picked up the "Double Trouble" achievement. It was bliss until we killed every gang member in Los Muertos. My friend (who was hosting the game) unlocked two achievements, both the "Los Muertos Intel Master" and "Los Muertos Cleanser". But there was a problem, I didn't receive any achievements. We then exited the game, I started a solo campaign by myself and noticed that all the progress I made in co-op with my friend was remembered except for how many gang members we found/killed. My agent's skill levels were retained, all agility orbs remembered, and even the supply points were marked as located. But it still showed that I haven't killed or found any of the 21 gang members and therefore haven't earned those corresponding achievements.

So fanboys, do you have a similar story or is this a weird one-off incident? Have you been playing co-op and earning achievements pertaining to taking down the gangs and its members? I've sent out a query to the powers that be and hopefully we will get some answers, because playing co-op and not earning certain achievements is ridiculous. Again, any information from you guys would help to get this issue figured out.