Does this mean that I'm really running into a pathological edge case in Perl5

Something like that.

You're using prototypes.

Ditch the ($@) on the function declaration, and everything will be fine. Perl will do what you think it should do.

sub foo {
   my ( $first, @other ) = @_;
   # do something to $first
   return( $first, @other );
}
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The rule I remember is this: "Only use prototypes if you are overloading CORE functions." That might not be sufficiently subtle, but it had stood me in good stead so far.