I just thought of something, GSteg--Do you have your AC on when you are trying to defrost the rear window? I know it sounds stupid, but bear with me: Dad used to sell Hondas, Honda tells their sales/technicians to tell owners to turn on the AC and heat when they defrost, and to use outside air (the AC takes moisture out of the air, the heat defrosts the windshield, etc)...This worked on my 97 Civic when I bought it in 97, my 99 Accord in 99, my 01 Accord in 01 and my new Accord now...
Now, in my Legend, I do the same thing to defrost the front windshield (heat with AC on)...And my rear defroster works well. Maybe it's only in my head, but I turned the AC off a couple days ago, and it *seemed* to take longer to defrost the rear--I don't know if there is a connection, but try it and let us know.