event.ctrlKey combinations blocked on Invision Power Board

Question

I am using the following code to add keyboard events to the Invision Power Board editor, but those combinations have been reserved for the Rich editor already. console.log(event); outputs on both Ctrl and B, but not Ctrl+B at the same time. The combinations are simply not read by the event handler on Plaintext mode.

The code works on this site and others. How can I add to them/unblock them on IPB?

document.addEventListener('keydown', function(event) {
    if (event.ctrlKey) {
        switch (event.keyCode) {
            case 66:
                event.preventDefault();
                console.log('b pressed');
            break;
            case 73:
                event.preventDefault();
                console.log('i pressed');
            break;
            case 85:
                event.preventDefault();
                console.log('u pressed');
            break;
        }
    }
}, false);