Mixins does not work inside option-set?

Enonic version: 6.8.0
OS: Linux

Inside my optionset I have a item-set with a single item which is a inline mixin.
The mixin fields are not displayed.

Just tested a mixin without the item-set, that did not work either.

The mixin is used many other places, so I don’t think thats the problem.

We reproduced this issue and registered the bug in our system.
The fix should be available in the 6.9 release.