Using these options:

$el.multiselect({
    disableIfEmpty: true,
    disabledText: 'Loading ...',
    nonSelectedText: 'None Selected'
})

I would expect buttonText to be 'Loading ...' iff the multiselect is disabled, and nonSelectedText to be used if it's not disabled and no items are selected. Currently, if disabledText and disableIfEmpty are set, nonSelectedText is ignored.