Bug report

Hello,
I encountered some confusing behavior when combining ChainMap with defaultdicts. Might be related to #23534
Specifically, iterating over the values or items of the ChainMap updates one of the underlying dictionaries, and returns the wrong result.
Just iterating over they keys or the dictionary directly produces the right results still and doesn't update the underlying dictionaries.

from collections import ChainMap, defaultdict

d1 = defaultdict(int, {'a': 1, 'b': 2})
d2 = defaultdict(int, {'c': 3, 'd': 4})
d3 = ChainMap(d1, d2)

print('Prior to iter')
print(d1)
print(d2)
print('After iter')
a = list(d3.values()) # Same result when calling d3.items
print(a) # Should return: [1, 2, 3, 4]. Returns: [0, 0, 1, 2]
print(d1) # Now: {'a': 1, 'b': 2, 'c': 0, 'd': 0}
print(d2) # Unchanged

Your environment

Tested on Python version 3.10.4.
Linux 5.13.0-41-generic #46~20.04.1-Ubuntu SMP
x86_64 x86_64 x86_64 GNU/Linux