Something has in fact been changed.
I tested this out for flyace earlier.
Attempted Santa Beard + Surfer Senshin.
Did not work, one item would be Deactivated as the other was Activated.
Attempted to use a Set as well, same result. Not sure if it is just these two particular hairstyles but flyace explained he had wore them previously and it is now not working.
Something changed, I am unaware of what however.