One can get around this problem by entering the following at the shell prompt.
pbpaste | sh
That's it. pbpaste is a shell command that writes the contents of the clipboard to standard output; piping it into the shell causes the shell to execute the command that was on the clipboard. pbcopy works in the other direction -- text sent to the standard input of pbcopy ends up on the clipboard. For example:
echo "Hello Aqua" | pbcopy
puts Hello Aqua on the clipboard.
[robg adds: We've discussed pcbopy and pbpaste before, but never in the context of using them to get the clipboard in X11.]

