Ah! I captured the traceback of a first bug using the command:

PCbuild\amd64\python_d.exe -m test -R 3:3 -u all -v --timeout=30 -r -F test_ttk_guionly

Output:

(...)
test_resize (test_ttk.test_extensions.LabeledScaleTest) ...
*** STACKTRACE - START ***
# ThreadID: 1216
File: "C:\haypo\2.7\lib\threading.py", line 774, in __bootstrap
  self.__bootstrap_inner()
File: "C:\haypo\2.7\lib\threading.py", line 801, in __bootstrap_inner
  self.run()
File: "C:\haypo\2.7\lib\test\regrtest.py", line 2024, in run
  self.dump_threads()
File: "C:\haypo\2.7\lib\test\regrtest.py", line 2050, in dump_threads
  self.dump_thread(stack)

# ThreadID: 2172
File: "C:\haypo\2.7\lib\runpy.py", line 174, in _run_module_as_main
  "__main__", fname, loader, pkg_name)
File: "C:\haypo\2.7\lib\runpy.py", line 72, in _run_code
  exec code in run_globals
File: "C:\haypo\2.7\lib\test\__main__.py", line 3, in <module>
  regrtest.main_in_temp_cwd()
File: "C:\haypo\2.7\lib\test\regrtest.py", line 2083, in main_in_temp_cwd
  main()
File: "C:\haypo\2.7\lib\test\regrtest.py", line 841, in main
  result = local_runtest()
File: "C:\haypo\2.7\lib\test\regrtest.py", line 827, in local_runtest
  testdir=testdir)
File: "C:\haypo\2.7\lib\test\regrtest.py", line 1042, in runtest
  return runtest_inner(test, verbose, quiet, huntrleaks, pgo, testdir)
File: "C:\haypo\2.7\lib\test\regrtest.py", line 1234, in runtest_inner
  huntrleaks)
File: "C:\haypo\2.7\lib\test\regrtest.py", line 1369, in dash_R
  run_the_test()
File: "C:\haypo\2.7\lib\test\regrtest.py", line 1355, in run_the_test
  indirect_test()
File: "C:\haypo\2.7\lib\test\test_ttk_guionly.py", line 37, in test_main
  *runtktests.get_tests(text=False, packages=['test_ttk']))
File: "C:\haypo\2.7\lib\test\support\__init__.py", line 1577, in run_unittest
  _run_suite(suite)
File: "C:\haypo\2.7\lib\test\support\__init__.py", line 1532, in _run_suite
  result = runner.run(suite)
File: "C:\haypo\2.7\lib\unittest\runner.py", line 151, in run
  test(result)
File: "C:\haypo\2.7\lib\unittest\suite.py", line 70, in __call__
  return self.run(*args, **kwds)
File: "C:\haypo\2.7\lib\unittest\suite.py", line 108, in run
  test(result)
File: "C:\haypo\2.7\lib\unittest\suite.py", line 70, in __call__
  return self.run(*args, **kwds)
File: "C:\haypo\2.7\lib\unittest\suite.py", line 108, in run
  test(result)
File: "C:\haypo\2.7\lib\unittest\case.py", line 393, in __call__
  return self.run(*args, **kwds)
File: "C:\haypo\2.7\lib\unittest\case.py", line 329, in run
  testMethod()
File: "C:\haypo\2.7\lib\lib-tk\test\test_ttk\test_extensions.py", line 184, in t
est_resize
  x.update()
File: "C:\haypo\2.7\lib\lib-tk\Tkinter.py", line 1023, in update
  self.tk.call('update')

*** STACKTRACE - END ***