Why do my lightmaps look blocky? (Picture)

Hello,

I've been getting amazing results in non-terrain lightmapping, but the same settings produce this ugly blocky result in any terrain map I do. I've had lightmaps work perfectly fine before, and have never seen this. Any ideas how this is happening and how to fix it?

PS -- yo ucan see the "live" shadows, not blurred at all, which disappear when I use forward rendering. I'm using deferred rendering so I can get read time shadows with the lightmapped statics.

Thanks!