[perl #132511] Binary assignment Z+= fails if it's the last thing in for loop

[brian d foy]

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I previously asked about this unexpected Z behavior on Stackoverflow
( https://stackoverflow.com/q/45001820/2766176 ).

I expected this to change several hash keys at once. It changes no keys:

    my $hash = %(
        wallet   => 100,
        gave     =>   0,
        received =>   0,
        );

    for ^1 { $hash<wallet gave> Z+= <-1 1> }

    dd $hash;

I get:

    Hash $hash = ${:gave(0), :received(0), :wallet(100)}

If I change that to add another statement it works:

    for ^1 { $hash<wallet gave> Z+= <-1 1>; True }

It also works if I take out the binary assignment:

    for ^1 { $hash<wallet gave> = $hash<wallet gave> Z+ <-1 1> }