Humbug fails with PHPUnit stderr setting

[ccwebdesign]

Question	Answer
Humbug ver.	1.0-dev
Adapter ver.	PHPUnit 5.7.21
Platform	Windows 10 Pro (conemu x64)
PHP ver.	7.1.8 w/ Xdebug 2.5.5

Ran into an issue with humbug starting with stderr="true" in phpunit.xml config despite passing tests. PHPUnit --tap didn't generate any errors either.

Humbug output

Tests must be in a fully passing state before Humbug is run.
Incomplete, skipped or risky tests are allowed.
The testing framework ran into a failure or error. Refer to output below.
Stderr:
   > PHPUnit 5.7.21 by Sebastian Bergmann and contributors.
   >
   > Runtime:       PHP 7.1.8 with Xdebug 2.5.5
   > Configuration: Y:\Apache24\temp\humbug\phpunit.humbug.xml

...

   > OK (125 tests, 304 assertions)
   >
   > Generating code coverage report in PHP format ... done

phpunit.xml

<phpunit bootstrap="bootstrap.php"
    colors="true"
    verbose="true"
    stderr="true">
    <testsuites>
...
    </testsuites>
    <filter>
        <whitelist processUncoveredFilesFromWhitelist="true">
            <directory suffix=".php">../src/</directory>
        </whitelist>
    </filter>
    <logging>
        <log type="coverage-html" target="./tmp/Report" lowUpperBound="50" highLowerBound="100"/>
    </logging>
</phpunit>

Removing the setting solved it.