IBus assigns Alt+Shift_L as hot key by default but the shortcut key cannot be used.
Sorry, it seems this problem exists with gnome-terminal only. I can use Alt+Shift_L with gedit, evolution, xterm. Closing this as not a bug. On the other hand, Shift+Alt_L does not work but probably it's not needed since we could use Alt+Shift_L. If users use the "Please press a key" dialog, it detects Alt+Shift+Shift_L but GTK2 event filter removes Shift modifier if the keyval is Shift_(L|R) so user need to uncheck the Shift modifier box by manual and change Alt+Shift+Shift_L to Alt+Shift_L .
Hmm.., thinking this again, it seems this problem can be fixed with IBUS_SNOOPER=1 with gnome-terminal. How important is this bug for f14?