I have Ctrl+Shift set to layout switch and press ctrl+shift+N (to open new Terminal or new tab in Opera) -- as a result I have my keyboard layout switched. This happens because Ubuntu (or XOrg?) change layout on key press instead of release and do not match layout hotkeys with application shortcuts. MS Windows do. If layout change hotkeys is pressed with another key this must be treated as application shortcut and layout must not be changed.
I've added this bug report about about a year ago to Ubuntu bugtrack:
Now it was commented by Gnome developer that "that's the way X
*** This bug has been marked as a duplicate of bug 865 ***