Unable to save a membership with a text price field

Same problem in 5.28 and master and can reproduce on dmaster.demo.civicrm.org. Or maybe I'm missing something.

1. Create a price set used for memberships.
2. Set financial type to member dues.
3. Add one text field (the default input field type).
4. Amount doesn't matter - put in some number.
5. Leave other fields at defaults.
6. Create a new membership.
7. Choose the price set.
8. Put in quantity 1.
9. Can leave the rest at defaults.
10. Click Save.
11. ERROR: Select at least one membership option.

It works with a radio field.