In "keys.xml", under the "Offsets" shortcuts, it shows "Ctrl (", "Alt (", and "Shift Alt (".

To generate a "Ctrl (" you need to press shift... but the other command makes a distinction.

Two solutions:

change keys.xml to say "Ctrl 9" change short cuts to handle "Ctrl 9" as well as "Ctrl (" (which is what the "Alt (" shortcut does.