you have to say what programs you are using to do this, because this obviously wouldnt happen if you had a rollover script and were just changing the image file, unless you overwrote the rollover as the same picture as the original.
I add the rollovers in imageready and yea it works just great but when I upload it to my site and edit the file using my html editor(frontpage) to edit the text the rollovers are no more and just become still images that do nothing when you roll over them