That's indeed a bit tricky. I think your best bet is to control this via the groups passed to the validate() call. You'd not redeclare the default group sequence for A, but instead either call validate(Default.class, Relaxed.class) (to validate all constraints) or validate(Default.class) (to validate all constraints except those in the Relaxed group).

For now I'll close this issue on the spec level as it "works as designed". But if you like, you could open an issue in the reference implementation (HV JIRA project) and we could explore a special pseudo group named ALL_UNASSIGNED or so, which, when passed to validate() would match all constraints not explicitly assigned to another group. This would help your case I think.