clipboard cut/paste problem

[plaut]

I'm having a problem getting emacs (21.4.1 under Linux) to import text
from other applications via cut/paste.  I have the following in my
.emacs:

(setq-default x-select-enable-clipboard t)
(setq interprogram-paste-function 'x-cut-buffer-or-selection-value)

Pasting (e.g., with yank) from other programs via the clipboard works
fine *until* I cut something to the clipboard from within emacs (e.g.,
with kill-line).  From then on, emacs only pastes from its own cut
buffer, not from the clipboard.

Any suggestions?