Still waiting to hear back, but I think there's a bug in TANGENT_SPACE_ROTATION

This only affects people who are still trying to do tangent space operations, but the code should normalize the vectors before construction

So, this is the code you should want.
float3 binormal = cross( normalize(v.normal), normalize(v.tangent.xyz) ) * v.tangent.w;
float3x3 rotation = float3x3( normalize(v.tangent.xyz), binormal, normalize(v.normal) );