In Settings > Keyboard > Application Shortcuts for the Print button (or any other button) paste the command xfce4-screenshooter -r (-r means --region). Now when pressing the Print button, a screenshooter process will start after few seconds (see system monitor), but won't appear on screen and won't do the region command. Executing xfce4-screenshooter -r from the console or a launcher button works properly. The problem is only with the shortkey. Shortkeys for other screenshooter options (like -f for fullscreen or -w for window) do work properly. I think (am not sure) that it appeared since the xubuntu 9.10 update. Confirmed on another xubuntu 9.10
Thanks for spotting this, I just fixed this issue in git master. The escape shortcut to cancel the operation is still not usable as I can't grab the keyboard in that case. commit 5854a53d8168fe1e2fedcf4c3e2be1261e027e2e Author: Jérôme Guelfucci <jeromeg@xfce.org> Do not check for grab status when not composited.