Well, a big duh on my part - I paid more attention last night and I had some streetlamps doing it too, but hadn't really noticed that before (?). I think maybe the RainX is thicker on certain parts of the windshield, and/or it is just certain viewing angles and light intensities, because not everything yields a double image. Slightly annoying, but not a big deal really, considering in the rain I usually don't even need my wipers. :-)