Excel is changing my dates

We have one column of dates in format of mm/dd/yyyy, next column of type of action or purchase, next column dollar amount, etc. When we sort the date column, excel would actually change some of the dates. I posted this on another message board and someone suggested highlighting everything, not just the date column, and that seemed to do the trick. I don't know why, and that bothers me, but I'm satisfied for now to be bothered and have the problem solved. Thanks for your reply, though.

TJ