FC3 slow X perfomance over ssh

[Paul19223 at yahoo.com]

Since upgrading from FC2 to FC3, remote X applications have slowed 
tremendously.  Before, apps like kmail were a bit laggy, but usable.  Now I 
can watch it paint the windows piece by piece.  Copying a line of text from 
a remote app caused my local X desktop (also running FC3) to lock up for 
over a minute.

Possibly related to this are a bunch of X errors like
 X Error: BadAtom (invalid Atom parameter) 5
  Major opcode:  18
  Minor opcode:  0
  Resource id:  0x188
These are printed continuously in the ssh window.

I'm using ssh -X -C -2 -l <username> <hostname> to log in, same as before.