There seems to be an issue with categories after a 2.6 upgrade. I've noticed a lot of threads in the forum about category names, descriptions and ID numbers that are missing after people have upgraded, and encountered a similar problem myself.
I'm in the process of switching to a magazine style theme. The information is ordered with query_posts functions which refer to specific category ID numbers. There used to be a field in Manage > Categories for the ID number, but I don't see that in the upgrade.
I've used MySql to access the wp_term_taxonomy, and added the Cat ID numbers to the description. I can see them under manage categories now, so basically I can just get on with tweaking my new theme, but this sure seems an inelegant workaround, and I wonder what if I'm missing something here. Are the Cat ID numbers really not there anymore, or is this a bug?