WebPlus X6: Rollovers broken by X6

I searched here for a reason this might happen, but found nothing:

I upgraded from X2 to X6, and today for the first time since upgrading, I had to alter my home page by simply removing the link to a sale that's ended. I uploaded the altered page, checked in several browsers, and this showed broken rollover images. After checking in all rollover setups and finding them correct, I tried various things, none of which worked. I did check on the server to make sure all the images were sitting there, and they were. Finally, I chose the upload option that checks for missing files, and that fixed the problem. Obviously, the X6 version of the page had broken the linkages.

Does anyone know why this would happen? Does it mean that any page containing a rollover created in X2 will be broken if I attempt to change anything on that page?

Thanks for any insight you can offer.