Please have a look at this jsFiddle:
With the prompt option on, the multiple selection gets messed up.
@ebryn Can you take a look at this?
I think that it doesn't make sense to use a prompt in multiple selection mode. I'm thinking prompt support should be disabled when multiple selection is enabled.
Good point, maybe just disable and update docs respectively.
I'm in favor of disabling prompt in multi-selection mode. I can't figure out how it would work anyway.
Disallow using a prompt on multi-select inputs - Fixes #881