I think you're running into a Perl bug. Looking at the uni/class.t unicode test in Perl, it uses fully qualified names for its classes when specifying the intersection/inclusion:

sub MyUniClass {
  <<END;
0030    004F
END
}

sub Other::Class {
  <<END;
0040    005F
END
}

sub A::B::Intersection {
  <<END;
+main::MyUniClass
&Other::Class
END
}
[download]

I understand that the Unicode engine wants fully qualified names because it is hard to determine relative to where an arbitrary string specified relative names, but Perl shouldn't exit with an internal error but tell/warn you that it interpreted all relative class names as absolute below main:: or that it can't do that.

Before you raise a bug for Perl, please check that you're running at least 12.2, as that bug might have been fixed in the meantime.