Nope, all vertices are already welded, and smoothing groups are the way they should be. Those were the things I've checked in the first place. Seems like long narrow polygons are the thing here.
Regarding your bug - Jeez no, I've hadn't encountered that bug. Maybe, that's because I don't bake textures themselves, I'm using Corona to generate lightmaps only. As for suggestions - seems like a real bug in renderer itself. Maybe, it has something to do with the virtual camera used to RTT (there is one, I guess). Or, if it was realtime rendering, I'd say it's definitely about anisotropic filtering or mipmaps. Anyway, I believe Corona Team knows better :)