From @masak

$ perl6 -v
This is perl6 version 2012.07-208-gb87659a built on parrot 4.5.0
revision RELEASE_4_5_0

$ cat script
use A;

sub MAIN {
  say "script's MAIN";
}

$ cat lib/A.pm
class A {
}

sub MAIN {
  say "A's MAIN";
}

$ perl6 -Ilib script
A's MAIN
script's MAIN

S06 is pretty clear that A's MAIN shouldn't be invoked in this case​:

<http://perlcabal.org/syn/S06.html#Declaring_a_MAIN_subroutine>

"This call is performed if and only if [...] the compilation unit was
directly invoked rather than by being required by another compilation
unit"

From @moritz

Fixed now, and tested in S06-other/main.t.

@moritz - Status changed from 'new' to 'resolved'