WiX v3.0.4206.0 bad, WiX v3.0.4207.0 better.
An MSBuild debilitating bug was accidentally introduced in WiX v3.0.4206.0. We got a fix in later that day and I just pushed a new build, WiX v3.0.4207.0. In case you pulled down 4206 thinking you were getting much goodness, you didn't... 4207 is much better. <smile/> Sorry for the trouble.