Was a solution found to this?
If the multi select field is set to required.
It seems to make the selection on a multi select lookup but it doesn't move the selection out of the left hand column.
If you then move the same item from the left hand column into the right, it re adds it and then you are able to apply the newform item.
When you check this item it the multi selection appears like: option 1, option 1, option 2 (1 of the 'option 1''s being what you moved over)
If you simply try and apply the newform item without changing anything, then you will receive the message about you must specify a value etc.
Tried this in IE and Firefox, with names and ID's. Same problem.