I use IPython very frequently and happily. Somehow, cutting text from the shell using the keyboard shortcut, Ctrl-X, is broken. Actually, I have a few different installations of IPython. In some of the installations, the shortcut works; in the others, it doesn't work.
What might be the reason for this? Where should I look into?
You say you have multiple instances installed -- are these all on different machines? What operating system(s) are they running? If you access them remotely, what operating system are you running?
Do you get to them using ssh? Do you run something like screen, either locally or remotely, or both? There are lots of things that can interfere with your terminal settings, especially when you're working remotely.
I'm almost certain that iPython doesn't have anything to do with it -- though you might want to check the version numbers, to see if working and non-working environments are running different versions.
More likely, it is something in the terminal emulation layer, but you'll likely have to do some detective work of your own to find out what piece is causing it.
Take it one step at a time -- try to cut from a local shell, to make sure that works. Then connect to a remote machine, and cut from that shell. Start screen, if that's your normal way of doing things, and test from that shell. Then start ipython. If it stops there, then see if you can find another application on the same machine that's linked against gnu readline, and try that. You may find that none of the console apps cut proplerly on that machine, or you may find that they work, but not under screen. Or you may find that something in the terminal settings stops everything from working as soon as you ssh in.
You may also have some luck. if you can find out what terminal the remote machine thinks you are using ( echo $TERM ) by copying the termcap file from a working machine to one that doesn't. That's a bit more involved for these forums, though -- I'd repost at that point on serverfault.com or superuser.com
I hope that at least gives you a starting place -- terminals are finicky, and difficult to get right. Most people seem to not bother, as long as everything mostly works.