I think it's just new threads getting censored in ORP, not posts to an existing thread.

There is a thread about charging a fee to stop ads which has become a kind of unheralded thread about these "sponsored links" between posts, and my posts (and others) about getting rid of ads in Firefox got through.

This is a private board so censorship by the owner is both allowed and completely valid, but doing it secretly seems a bit off target. Also, with this approach, the whole ORP forum will stagnate. Maybe that's the intent.