But I guess you can use two MSs, one for transmit and one for receive to overcome this limitation. Is there any problems with this approach other then good clock synchronization?

You need a very good clock sync :) But that's something that could be tried I guess.

PS Looking at pictures of ip.access Nanostation we didn't find any duplexers. How does it work then? Or have we just missed duplexers on the photos?

Nope, no duplexers.

There is a TX antenna and a RX antenna. I think they are patch antenna that don't radiate sideways so that they don't leak into one another. There is also a massive chunk of metal between them to isolate :)

Sylvain