[Seaside] Surprised at callback/livecallback on multiselect

[Steve Aldred]

Just an FYI for those playing in the area.

 From a bit of research into liveCallback it appeared that the callback 
block would not get called. The tests also seem to indicate this.

However if the form containing the multiselect gets submitted then the 
callback fires even though the liveCallback has already fired. I guess 
it makes sense but it wasn't what I expected.