Looks like Seam conversation scope is stored somewhere in the view state, and therefore is initialized only after component tree. So binding to conversation scoped-bean most likely causes failure.
I would recommend to use request or session scoped bean.
That is not RichFaces issue but Seam's. I may be wrong, so ask in Seam forum to know for sure.
I just had a similar problem, I solved it by outjecting the binding object.
There is actually an aptly named chapter in the seam docs for this, which I completely missed ;)
The seam forum post is here: