sub f {
    my $x = shift;
    *z = $x; 
}

f({}); 
f();
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Dave Mitchell solved this within a week and gave this description: "the second call to f() has $x as type RV (due to the previous call), but !ROK - due to the undef assignment. sv_setsv_flags() didn't check for ROK in this context." This was discovered while writing Object::Lexical. It stuffs closures into a stash created to represent an object - each object is its own blessed stash. I assumed (incorrectly) that the problem had something to do with blessing stashes. The fix is in 5.8.1. Hats off to the Perl 5 Porters! You guys rock! -scott