Radio buttons and checkbox fields were never intended to be used with variable length value lists.
There are ways to use scripts and a portal to simulate this effect, however... Each portal record would list one value and clicking a button in the portal row selects that value, adding it to the list of values in a field defined in the parent record or removes it if it was previously selected. Conditional formatting can be used to show which values are currently selected.
I thought there was something wrong with my layout... I currently exploring portals.