Shift X reaches markets that are not on your screen. The
modifier is the friction between one ladder and the whole book, and it is
deliberate.
The cancels under the cursor need the pointer over a ladder. That is how the
desk knows which one you mean when several are open.
Changing them
Every key can be moved in Settings, Shortcuts: click the key, then press the
one you want. Taking a key that is already in use swaps the two rather than
leaving you with a shortcut that does nothing. 
