To answer mdz's question, I do not have a problem with two Ubuntu machines. The local machine serving X11 is Feisty; the remote machine serving sshd is Dapper.
Local desktop relevant packages: xorg-7.2-0ubuntu11 openssh-client-4.3p2-8ubuntu1
Remote desktop relevant packages: libx11-6-1.0.0-0ubuntu9 xauth-1.0.1-0ubuntu1 openssh-server-4.2p1-7ubuntu3.1 vim-gtk-6.4-006+2ubuntu6
To answer mdz's question, I do not have a problem with two Ubuntu machines. The local machine serving X11 is Feisty; the remote machine serving sshd is Dapper.
Local desktop relevant packages: 7.2-0ubuntu11 client- 4.3p2-8ubuntu1
xorg-
openssh-
Remote desktop relevant packages: 6-1.0.0- 0ubuntu9 1.0.1-0ubuntu1 server- 4.2p1-7ubuntu3. 1 6.4-006+ 2ubuntu6
libx11-
xauth-
openssh-
vim-gtk-