Now that I've seen this once, I'm noticing it anytime the camera is pointed in that direction, regardless of where I am on the map.

EDIT: Same issue is visible in the Crucible map as well, so it is probably not a map related issue, but rather something weird when the camera is pointed in that specific angle.

I see this as well.  My diagnosis is that when the game computes the area that needs to be covered by the shadow map, it somehow fails with certain camera angles and produces a hugely oversized area, thus enlarging the pixel size of the shadow map.  How it fails, I can't say for sure - perhaps something to do with tan(x) tending to infinity when x nears plus or minus 90 degrees?

My system: WinXP SP2, GeForce 7900GTO, 178.24

Settings: 1680x1050, high detail, no AA

I don't think this is a driver issue though.