5.3-BETA5 X weirdness

I'm seeing some X weirdness on 5.3-BETA5.

Running X, I ssh to some other machine (doesn't matter what, the machine
happens to be running 5.1-RELEASE).  Then run xterm on the remote machine.  If
I left-mouse-button select text in the xterm window, and the
middle-mouse-button drop it in any other window, I get this error:

X Error of failed request:  BadAtom (invalid Atom parameter)
  Major opcode of failed request:  18 (X_ChangeProperty)
  Atom id in failed request:  0x104
  Serial number of failed request:  151
  Current serial number in output stream:  153


Any idea how to fix?