Cannot set default value for enrollment attribute

For an enrollment flow attribute such as Affiliation (CO Person Role), bring up the edit view, then choose a default value of "Member". Uncheck "Modifiable" and check "Hidden". Then click SAVE.

Then bring up the edit view again to find that there is no default value, and Modifiable is checked again.

This is seen in develop at commit 5e51357b8e813df278b274db9a88013960640574.