This test relied on short-circuiting details of dictobject.py to avoid

This test relied on short-circuiting details of dictobject.py to avoid
crashing, and indirectly on the fact that hash codes in
random.randrange(1000000000) were very unlikely to exhibit collisions.
To see the problem, replace this number with 500 and observe the crash on
either del target[key] or del keys[i].

The fix prevents recursive mutation, just as in the key insertion case.