Hi;

The post type = page is assigned to a blog category which we chose.

It's kinda wrong because when you chose the type of url "Subcat/post-name" in blog's settings, the url of the page consists the category, but obviously the page isn't in that category if you browse it.

I think that pages should have a separate, hidden, system category (named "pages", for example :P)

Also, when changing post to page, an error occurs. :)