old comments with new date??

I’ve got a weird problem.

I have old posts with old comments. Lets say that old post is from the 14th of February 2011. When i bring back up and republish it for today 3rd of October 2011, then the date of the comments are set to the new date. I didnt have this problem before, but didnt notice when it changed. When i go into the edit section of the comments for the new republished post i can still see the old date.

help ??