Bug causing some custom fields to not appear in board view?

I see the option at the folder level to choose which elements to "show on cards" when the folder is in board view. I have two custom fields available to choose from. One of those custom fields is a date field and the other is a formula (measuring elapsed time in days). Choosing to show the date field works as expected (I see the date with its field label on the cards) but choosing to show the formula-based custom field doesn't seem to do anything. When clicking into cards (tasks), I can see the formula-based custom filed is correctly populated.