Custom Field Filter: Displaying specific values

-- HikaShop version -- : 2.4.0
-- Joomla version -- : 3.4.1
-- PHP version -- : 5.3.10
-- Browser(s) name and version -- : Firefox 38.0.5

I want to restrict a custom checkbox filter to only the values I choose, but saving erases my choices.

I have created a custom field called "Features" and populated the values like this:

Then I created a filter based on this field:


Here, you can see that the Values entered match the "Values" field from the custom field. In this example, I only want the filter to show 2 choices.

But when I save, it erases the Values:


I know that numbers are accepted, but I would prefer that the values stay as alphanumeric values. Is there a way around this?
I also am aware of Dynamic Display, but this solution won't help because the data will come from an external source and sync automatically with the shop. It's very possible that products will have certain Features that we don't want to show as a Filter.