Other field is shown by default drop down widget if no default value is set

i'm using the drop down widget for a select list field, which the field is not required
if the field default value is empty (none), on the first display of the node form, the other textfield is shown
but then the other textfield is hidden by JS correctly when user changes select list value,
and other textfield is hidden if user select none on the select list

on first display of node form,
if user makes no change to the select list, i.e. leave it as default value = none,
then enter something in the displayed other textfield and save,
the other value is not saved and the field value is still saved as none

i believe this behavior is confusing to user,
and easily makes user believes that the value is saved, even though it's not
a better way would be that if default value is none, hide the other textfield
so that user has to intentionally select "other" from select list in order to enter a custom value