Thanks, Ivan, that change fixes it for me, too.

I checked with a more recent revision and build:

$ hg identify
265644bad99e+ tip
$ ./python.exe --version
Python 3.6.0a4+
$ 

Confirmed that it still exhibited the same behaviour as before:

$ ./python.exe -m test test_ast
Run tests sequentially
0:00:00 [1/1] test_ast
1 test OK.
Total duration: 0:00:06
$ 

$ ./python.exe -m test --coverage -D`pwd`/coverage_data test_ast
Run tests sequentially
0:00:00 [1/1] test_ast
Assertion failed: (line > 0), function _PyCode_CheckLineNumber, file Objects/codeobject.c, line 717.
Fatal Python error: Aborted

Current thread 0x00007fff7b5a7000 (most recent call first):
  File "test", line 0 in <module>
  File "/python-dev/cpython/Lib/test/test_ast.py", line 559 in test_level_as_none
  File "/python-dev/cpython/Lib/unittest/case.py", line 600 in run
  File "/python-dev/cpython/Lib/unittest/case.py", line 648 in __call__
  File "/python-dev/cpython/Lib/unittest/suite.py", line 122 in run
  File "/python-dev/cpython/Lib/unittest/suite.py", line 84 in __call__
  File "/python-dev/cpython/Lib/unittest/suite.py", line 122 in run
  File "/python-dev/cpython/Lib/unittest/suite.py", line 84 in __call__
  File "/python-dev/cpython/Lib/unittest/suite.py", line 122 in run
  File "/python-dev/cpython/Lib/unittest/suite.py", line 84 in __call__
  File "/python-dev/cpython/Lib/test/support/__init__.py", line 1709 in run
  File "/python-dev/cpython/Lib/test/support/__init__.py", line 1810 in _run_suite
  File "/python-dev/cpython/Lib/test/support/__init__.py", line 1844 in run_unittest
  File "/python-dev/cpython/Lib/test/libregrtest/runtest.py", line 179 in test_runner
  File "/python-dev/cpython/Lib/test/libregrtest/runtest.py", line 180 in runtest_inner
  File "/python-dev/cpython/Lib/test/libregrtest/runtest.py", line 144 in runtest
  File "<string>", line 1 in <module>
  File "/python-dev/cpython/Lib/trace.py", line 469 in runctx
  File "/python-dev/cpython/Lib/test/libregrtest/main.py", line 330 in run_tests_sequential
  File "/python-dev/cpython/Lib/test/libregrtest/main.py", line 406 in run_tests
  File "/python-dev/cpython/Lib/test/libregrtest/main.py", line 466 in _main
  File "/python-dev/cpython/Lib/test/libregrtest/main.py", line 446 in main
  File "/python-dev/cpython/Lib/test/libregrtest/main.py", line 508 in main
  File "/python-dev/cpython/Lib/test/__main__.py", line 2 in <module>
  File "/python-dev/cpython/Lib/runpy.py", line 85 in _run_code
  File "/python-dev/cpython/Lib/runpy.py", line 184 in _run_module_as_main
Abort trap: 6
$ 

I applied the change you suggested, and this was the result:

$ ./python.exe -m test --coverage -D`pwd`/coverage_data test_ast
Run tests sequentially
0:00:00 [1/1] test_ast
1 test OK.
lines   cov%   module   (path)
  556     1%   _collections_abc   (/python-dev/cpython/Lib/_collections_abc.py)
  147    25%   _weakrefset   (/python-dev/cpython/Lib/_weakrefset.py)
   96    16%   abc   (/python-dev/cpython/Lib/abc.py)
  156    66%   ast   (/python-dev/cpython/Lib/ast.py)
  418     1%   codecs   (/python-dev/cpython/Lib/codecs.py)
  692     0%   collections.__init__   (/python-dev/cpython/Lib/collections/__init__.py)
  166     8%   contextlib   (/python-dev/cpython/Lib/contextlib.py)
  318    22%   dis   (/python-dev/cpython/Lib/dis.py)
   74     5%   genericpath   (/python-dev/cpython/Lib/genericpath.py)
  103     2%   importlib.__init__   (/python-dev/cpython/Lib/importlib/__init__.py)
 1776     0%   inspect   (/python-dev/cpython/Lib/inspect.py)
 1228     0%   locale   (/python-dev/cpython/Lib/locale.py)
  170     0%   multiprocessing.process   (/python-dev/cpython/Lib/multiprocessing/process.py)
  612     1%   os   (/python-dev/cpython/Lib/os.py)
  687     0%   platform   (/python-dev/cpython/Lib/platform.py)
  313     5%   posixpath   (/python-dev/cpython/Lib/posixpath.py)
  435     1%   sysconfig   (/python-dev/cpython/Lib/sysconfig.py)
  336     1%   test.libregrtest.main   (/python-dev/cpython/Lib/test/libregrtest/main.py)
  174    29%   test.libregrtest.runtest   (/python-dev/cpython/Lib/test/libregrtest/runtest.py)
  197    27%   test.libregrtest.save_env   (/python-dev/cpython/Lib/test/libregrtest/save_env.py)
 1341     3%   test.support.__init__   (/python-dev/cpython/Lib/test/support/__init__.py)
  870    98%   test.test_ast   (/python-dev/cpython/Lib/test/test_ast.py)
  461     0%   trace   (/python-dev/cpython/Lib/trace.py)
  285     2%   traceback   (/python-dev/cpython/Lib/traceback.py)
  824    20%   unittest.case   (/python-dev/cpython/Lib/unittest/case.py)
  329     8%   unittest.loader   (/python-dev/cpython/Lib/unittest/loader.py)
  134    20%   unittest.result   (/python-dev/cpython/Lib/unittest/result.py)
  222    44%   unittest.suite   (/python-dev/cpython/Lib/unittest/suite.py)
  134     0%   unittest.util   (/python-dev/cpython/Lib/unittest/util.py)
  384     6%   weakref   (/python-dev/cpython/Lib/weakref.py)
Total duration: 0:00:09
$