I succeeded to reproduce the bug, but only when running the -jN option, like:

./python -m test -j2 -R 3:3 test_zipfile

I reduced the test to:

./python -m test -j2 -R 3:3 test_zipfile -m test_random_open

This test heavily use random.randint().

In fact, the bug doesn't come from test_zipfile, but it's an issue Python singleton objects. There is a bug in regrtest which doesn't call warmup_caches() in worker processes when using the -jN option (multiprocessing mode).

My PR https://github.com/python/cpython/pull/2220 should fix the bug.

Sadly, I didn't backport test_regrtest functional tests from master to 3.5 yet: see bpo-30383.