actually, it's not one stubborn emulator. it's the whole meaning of file extensions:
- lnx was for original headered dumps
- lyx was for unheadered dumps

if no-intro tries to impose a faulty standard it's not MAME's fault, and they should rethink their approach.
they tried as well to impose headerless NES roms, which are simply unusable with emus since they miss all the hardware info needed to make them run, with the simple result that they needed to code with Roman a "skip-header in rom manager" workaround to avoid becoming ridiculous wink
I don't see why the same approach cannot be followed here, or the extension to be changed to .lyx...

the only result as things stand is that people remove header from some .lnx dumps which need it and we potentially lose info until some new dumper spend his time re-dumping the carts