logback.xml not found when running under Ant task

Logback uses the thread context ClassLoader to look up logback.xml but the Ant uses a custom ClassLoader that does not have the task JAR in its classpath, as a result logback.xml is never found.

That is, getClass().getClassLoader().getResource("logback.xml") works
Thread.currentThread().getContextClassLoader().getResource("logback.xml") does not.