Comment 2 for bug 604143

I noticed the same thing.

You can fix it with a grep -v

xprop -id `xprop -root | grep -v CUT_BUFFER | awk '/_NET_ACTIVE_WINDOW/ {print $5; exit;}'`...

Of course this will then break, if your window title happens to be CUT_BUFFER, so you really can't win :)