I'll bring this to the dev's attention, but in the meantime can you save the screenshot as png? jpg is lossy and it's hard to tell what degree if the graininess in that format is due to the problem you're describing as opposed to the format itself.
I'm seeing some of this in my IE7 testing, although the avatar customizer does not work in IE7 at the moment; I'm going to be checking IE8 shortly as well. I'll let you know more as I find out.