That's nothing new. Greg mailed me a chip for 41-cents using cro-nel (nice and even). I'm not surprised that the PO doesn't bother with the surcharge of a mere letter. Earlier, there were many posts here about different post offices treating the same thing differently. ... ...... I bet they will often hit you with the 17-cent surcharge if you hand the letter to a clerk but not bother if it is dropped in a postal box.
Best,
Robert