Yeah, The behaviour of ($foo = 1) . ($foo = 2) . ($foo = 3) used to be roughly equivalent to

my $x = "";
$x .= ( $foo = 1 );
$x .= ( $foo = 2 );
$x .= ( $foo = 3 );
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But now, it's roughly equivalent to

my $x = join("",
   ( $foo = 1 ),
   ( $foo = 2 ),
   ( $foo = 3 ),
);
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In both cases, $foo itself is being put on the stack. The difference is when it's used (before it has a chance to be changed by later assignments, or after).