load_dll now does a find_dll_file and sees "L:\temp\IXP000.TMP\msi.dll" . sets filename to "L:\temp\IXP000.TMP\msi.dll" and compares "L:\temp\IXP000.TMP\msi.dll" for the loadorder.
Try using *msi=b in the dll overrides. That makes it apply to any path.
Yes this is very unintuitive, badly documented etc, and I'd prefer the meaning to be inverted. But, that'd break old configs.