[Jason says it looks like another VC++ toolchain bug is being hit again.] Is that what you're talking about?

Yeah. There are issues that Visual Studio has with parallel builds. So to speed up our build time, we do a lot of compilation in parallel. And Microsoft really doesn't support that very well, at least it seems. So we have things like that to work around. Sometimes it's just a simple restart of one of the build slaves, and sometimes we have no idea why.