Include paths (build file) not working

I cloned Allegorthmics branch of 4.9 to alter the Substance plugin. To do this, I temporarily moved the plugin to a project and built, but none of the includes are working.

For example, the build file:
Substance/Source/SubstanceCore/SubstanceCore.Build.cs
contains this line:
PrivateIncludePaths.Add(“SubstanceCore/Private”);

Yet the file at:
Substance/Source/SubstanceCore/Private/framework/details/detailscomputation.cpp
contains:
#include “framework/details/detailscomputation.h”

But it can’t locate that header file unless I make the path relative (which gets ugly!), which I thought the build file configuration was meant to help you avoid. Has anyone else had problems like this?