The Portland FSDO is wrong.
You have Pvt glider which includes LSA glider aircraft, to include a self launch glider with a self launch endorsement.
Pay attention to the differences between endorsement and rating.

Additional LSA ratings, such as powered parachute, weight shift ultralight, or Piper J3 cub requires the Two CFI and an 8710-11 filed with OKC.
I believe you will need to fly the additional LSA aircraft with the 10,000 MSL and other LSA limitations.

BillT