When using xdist, warnings are not associated with tests in the report

Given the example test from the docs:

import warnings

def api_v1():
    warnings.warn(UserWarning("api v1, should use functions from v2"))
    return 1

def test_one():
    assert api_v1() == 1

When this test is run without xdist, the warning report includes the test's node_id:

❯❯❯ pytest
============================= test session starts ==============================
platform linux -- Python 3.6.7, pytest-5.2.1, py-1.8.0, pluggy-0.13.0
rootdir: /tmp/warn
plugins: forked-1.1.1, xdist-1.30.0
collected 1 item

test_warn.py .                                                           [100%]

=============================== warnings summary ===============================
test_warn.py::test_one
  /tmp/warn/test_warn.py:6: UserWarning: api v1, should use functions from v2
    warnings.warn(UserWarning("api v1, should use functions from v2"))

-- Docs: https://docs.pytest.org/en/latest/warnings.html
======================== 1 passed, 1 warnings in 0.01s =========================

Running the same test with xdist, the node ID test_warn.py::test_one disappears:

❯❯❯ pytest
============================= test session starts ==============================
platform linux -- Python 3.6.7, pytest-5.2.1, py-1.8.0, pluggy-0.13.0
rootdir: /tmp/warn
plugins: forked-1.1.1, xdist-1.30.0
collected 1 item

test_warn.py .                                                           [100%]

=============================== warnings summary ===============================
test_warn.py::test_one
  /tmp/warn/test_warn.py:6: UserWarning: api v1, should use functions from v2
    warnings.warn(UserWarning("api v1, should use functions from v2"))

-- Docs: https://docs.pytest.org/en/latest/warnings.html
======================== 1 passed, 1 warnings in 0.01s =========================

This makes it difficult to trace back which test caused which warning in the CI system.

Ubuntu 18.10

Python 3.6.7

apipkg==1.5
atomicwrites==1.3.0
attrs==19.3.0
execnet==1.7.1
importlib-metadata==0.23
more-itertools==7.2.0
packaging==19.2
pkg-resources==0.0.0
pluggy==0.13.0
py==1.8.0
pyparsing==2.4.2
pytest==5.2.1
pytest-forked==1.1.1
pytest-xdist==1.30.0
six==1.12.0
wcwidth==0.1.7
zipp==0.6.0

Reproduce the warning example in test_warn.py with pytest both normally and with xdist, comparing the warnings summary. Trace how xdist handles warning reports and test node IDs; done when the xdist report retains test_warn.py::test_one for the warning, with coverage for both execution modes.