Since the beginning, the "none" value (aka no value is selected for this field) has a special id = 100.
However nothing prevents the real value to get the same id 100. This produces weird behavior:
(severity is not really empty)
Furthermore if you change the color of "Low impact", this has repercussions on the display of None:
I currently have no idea how to fix that for existing instances. For new instances, we could force the auto_increment to start at 101.