I have a strange error, and I cannot track it down.

I have a fight.ash relay script that adds a macro button. This submits a combat macro for the fight. It works just fine, with one singular exception.

When I fight Somerset Lopez, Demon Mariachi (end of the Nemesis quest for AT), it returns this error:
Macro Aborted, couldn't find mark named "__sub__0end".

The mark "__sub__0end" does not appear in my consult script, or my relay script, or in any of the files in my KolMafia folder.
I have no combat macros defined on my account.
Submitting the macro through run_combat() works fine.

This is driving me nuts! Any idea where it might be coming from?