Hello Alan,
I am really sorry for the delay of this reply as it is a weekend for us here. I have tried to replicate this on your site but wasn't able to. I tried to edit the post Rome 2003 and this is what I am seeing:
Editing Post:
1. The post cover is still there,
http://take.ms/zPztE
2. I was able to to change the category of an existing post,
http://take.ms/KFSiw
New Post:
1. I was able to change or add category to a new post that I am creating,
http://take.ms/Vqhu6
Am I testing this wrongly?