The short answer to your question is that the way for and map alias $_ isn't orthogonal (map does a straight alias, for does magic). This behaviour is known about, so not really a bug. I think it's intentional DWIMery as it's idiomatic to modify the current topic ($_ in this case) in for whereas it's very bad form to modify the topic in map. Perhaps it's worth noting in the map docs this effect of aliasing an empty $_ makes it READONLY, but I somehow doubt it would be applied ala doctor, it hurts when I do this ....

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broquaint