We upgraded our servers to W2008r2 64 bits and rdesktop clipboard support stop working. Workstations are using ubuntu lucid taht comes with rdesktop 1.6 so, we downloaded latest rdesktop version 1.7.1 but it had the same behaviour. For testing purposes, we install a w2008 32bits (not R2) and rdesktop clipboard redirection worked perfectly.
It's easy to reproduce. We reinstalled a new W2008r2 in a virtual machine, and update it or not, rdesktop have problems redirecting clipboard.
We tried different rdpclip.exe versions too (from vista, etc) with no success.