that is an interesting point, so the licence just states under validity:
"The privileges of the licence shall be exercised only if the holder has a valid medical certificate for the required privilege."
It does not states that the type rating need to be valid.
Also I checked with the FAA that they do not requiere a JAA medical, they told me a FAA medical is sufficient.
Initially I thought the same as you but could not find anything in writing.
Marcus