[junke]

In the standard it is not specified if such loops mutate or rebind, and you have to assume it doesn't rebind if you capture variables. I do think however that once you learn how it works it stops being a problem (in any case I can select the form, macroexpand it and it shows how it's implemented)

[varjag]

In theory sure. In practice it's easy enough to make this mistake mindlessly. I had this happen to me after many years of practice just this year (in an elaborate extended LOOP form which has same semantics).