It seems that some people are using CataBlog fine in WordPress 4, while I think others have had problems. I would suggest testing CataBlog with any future versions of WordPress and or your Theme before upgrading your "live site". The best way to do this is with a backup run locally on your own computer.
The new WordPress upgrade broke CataBlog, please do NOT update to WordPress 4.0 if you need to keep using CataBlog. I will look into the problem as soon as I can, but since it is freeware and I need to concentrate on my paying job, I won't be able to tell you how long until it is fixed.
Thanks again everyone for your patience and support of CataBlog, cheers!