I fixed the issue with keyboard input being disabled under certain circumstances. One of the commits in this request is the revert I did on my own end, not sure how to not include it in the request?

Anyways, the important piece is this:

on('mousedown.P' + CALENDAR.id,function(event){
    if ( event.target != ELEMENT ){
        event.preventDefault()
        event.stopPropagation()
       }
} )

It keeps the focus from being stolen from the input element, thus allowing keyboard input to remain.