"Extended post" is a cross-category post, posted in categories of Blog 2 and 3.

So, this is not a bug, as far as I can see.

Cross-category post :S

Where do you find out that, and/or how do you do that?

There is a param in one of the files in the conf folder. _admin.php or _advanced.php I think but I'm usually wrong. Several choices exist. Post in one category only, post in multiple categories in one blog, post in multiple categories in multiple blogs, and the very funky you can move a cat from one blog to another blog.

Yes but there is only one BlogID even though they are in categories of more than one Blog - this seems quite strange to me....

Plus shouldnt if this feature is enabled should we have all the blog's categories displayed when 'writing' a post, instead of just the selected one?

So the blogID thing. Each post is technically associated with a main category which in turn is associated with a blog. We think differently. We think of the blog first and the category second, but that's not how the database stores posts or how the code pulls them up. Secondary cats also have a blog associated, meaning you see stuff in both blogs. Technically speaking you are looking at a blog, but in fact you are looking at a collection of categories in that blog - and of course any post that has that category assigned.

With "$allow_cross_posting" set to 2 you will have all your cats of all the blogs you are authorized to post into displayed in the sidebar of the write tab. The top of the write tab will show all the blogs you're authorized to post in, and the only cats that have the box for selecting the primary category will be cats in that blog. All other blog cats will be available as secondary categories.

Oh and b2evo ships with "$allow_cross_posting" set to 1 AND has one sample post that acts as if the param is set to 2. At the demo (and any raw installation) you simply can't do what that one post does. You have to edit the _admin file to get that feature enabled.

BTW it is in conf/_admin.php.