Perfect! Change

-$obj->lf_int=444;
+sub lf_int :lvalue { $obj->lf_int }
+lf_int=444;
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and you get

Can't return a temporary from lvalue subroutine
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That's the bug. It's a spurious exception (not a warning!) when the temp has set magic.

Obscure, yes, but I want to change the lvalue ops to return a temp which would cause the following to give the same error:

sub foo :lvalue { substr(...) }
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