As you can see in the loom, an orphan mid layer trace is not flagged causing all manufactured boards to have the same invalid ISP header. The trace is routing under the component and yes, this is my own fault for not coming up to top layer before the pin connector (I was seriously tired) - but I would expect this to still be flagged as a DRC fail. [EDIT] - sorry, I kept referring to this as the JTAG header, but it just the ISP header https://www.loom.com/share/34563e45c9364fa6b723801c7f510de9