Collapsed custom field set for activities with a required radio makes case activity buttons seem disabled

Might be from the recent jquery radio validation update. Haven't followed it through yet. Not even sure if it's specific to radio yet.

1. Create a custom fieldset for activities.
2. Make it apply to all activity types (not relevant just makes this quicker).
3. Make it collapsed by default.
4. Add a radio field.
5. Make it required.
6. Administer - Customize - Display Prefs - Turn off popups (near the bottom). (Only relevant because then you can see the issue for all case activities - when it's on you only notice it for open case/creating a case.)
7. Create a case.
8. Fill out the client, subject, and case type but leave the collapsed custom field section collapsed.
9. Click Save. It appears as though nothing happened, but if you open the custom fieldset you can see why.