A little bit of more elaboration, if I may ask..
I got dumped to admin a WP site, which has been running for years and has been updated with ~20 plugins and a custom theme. (http://www.tuima.fi)
I installed the WP-HIDE-POST plugin and running to the same problem (I think), I can see the widget in the sidebar when posting a new post, but whether I cross all the 'hide' functions, it makes no difference - the post still shows on main page.
I'm thinking at this point that the theme is coming with a custom post function/name, but alas, I've no idea what it is or where to find it (or if it even exists!). Can you point me in the right direction, where I could find the custom post types name so I can try if I can get it work like that.
And, nope, never touched wordpress before I got this project, thus I'm a bit lost. Trying my best but, the code is a bit too messy for me :/
A few installed plugins that might also be the trouble? :
category posts widget
Any help would be greatly appreciated.