If an executable return value has a constraint and is marked for cascaded validation, cascaded validation will not happen if the constraint on the return value itself is invalid.

See MethodValidationTest#methodReturnValueValidationTargetsReturnValueAndCascadedConstraints()

I think the cause is that in ValidatorImpl#validateReturnValueForGroup() the following lines are before the cascaded validation but need to go after that (as is the case for parameter validation):

//stop processing after first group with errors occurred
if ( numberOfViolationsOfCurrentGroup > 0 ) {
    break;
}