Colour Flicker due to Sunlight?

I keep getting "seam flicker" when I align two prims side by side, despite the fact they're not overlapping. I've also noticed that it only occurs when the sun is at a certain angle, and when the sun moves to the other side of the two prims, the flicker problem transfers to the other side! It seems to me that it's due to the difference in lighting on the faces that *should* be completely hidden.

Can anyone confirm this? And are there any clever solutions? It's just occurred to me whilst writing this that I should maybe apply a transparent texture to the hidden faces. Hmm.

It can be a symptom of your video card not quite knowing what to do with parts of the image that are technically visible, but less than one pixel wide. Try applying a completely transparent texture to the sides of the wall pieces that meet.