each has a global effect because the counter is changed on the data structure, when it's used at several different code places.

From each docs:

> Each hash or array has its own internal iterator, accessed by each, keys, and values. The iterator is implicitly reset when each has reached the end as just described; it can be explicitly reset by calling keys or values on the hash or array.

IIRC is Data::Dumper resetting the counter internally.

see also do-not-use-each by Reini Urban.

Honestly I don't understand your intention, because Dumper is already recursively descending into the nested data structure. And those modules can't achieve it without using keys or values.

update

rephrased and added references.