The Line.Info.toString() has this check for the system package:
 328 String fullPackagePath = "javax.sound.sampled.";
 329 String initialString = new String(getLineClass().toString());
 332 int index = initialString.indexOf(fullPackagePath);
 334 if (index != -1) {

This check accepted packages which are not system packages, like this:
"bug.javax.sound.sampled"