Don't know if anybody has read: But apparently theres a glitch/bug associated with the latest patch. The solution right now? DON'T START YOUR LEFT FOR DEAD ONE COPY! *IF* you have any achievements you did not finish. It's reseting peoples achievement progress on zombie genocide and even the little zombie genocidist, along with surviving all campaigns on expert (which I am still missing the last one lol). I was at like 34k kills so I'm afraid to even boot it up to see if I was effected.
if you already got all the achievements in Left 4 Dead 1 It's no biggie, but if you were planning on going back to L4D1 to finish off achievements - don't till they fix the problem. I'm not sure if Avatar awards were reset on the patch for L4D2 but I noticed no issues with L4D2 with achievement progress.