Well, I'm not sure if this would help at all but, on classic iphone, the lag is really awful of course because your on an iphone, but when you cross levels of the gmap when there is very bad lag the gmap completely refuses to load and causes all the tiles to turn into the default grass tile. Players often call it "Lag grass". I think thats what you talking about
and fixing it, I have no idea. I usually just log off and back on.