In the example you gave, the library you were adding ("dummy mt") has a space in it. We don't handle that case - that was my point.
But "dummy mt" was injected by the broken configure logic, not by me. It was the SYMPTOM not the cause. So, I missed the point you were making.
However, your other note is also correct - the vpath builds need to be fixed with the other CMR.
Yup. Even at 2am I know enough about how things work around here to eventually find the "other CMR", once I knew in general terms what I was looking for.