defroster

I don't remeber this happening last winter, but lately when I turn on the rear defroster, it clears up the main part of the rear window but doesn't clear up the top part of the rear window where the lines on the window are a few inches narrower. Is the defroster only supposed to clear up the...

I've noticed my rear defroster doesn't do anything.. I can't remember if it ever worked since I haven't needed it that often. I'll be taking my car to the dealer of course but just wanted to give a heads up in case anybody else has noticed this problem.