Inspection overly aggressive?

Consider the following:

public abstract class Encoder {

public static Encoder makeStringEncoder() {
return new StringEncoder(); // I'm a naughty boy!
}

private static final class StringEncoder extends Encoder {...}
}

In Demetra 5661 the inspection "Class references subclass" flags the
indicated line.

Abstract classes offering factory methods is a common pattern and, if
the implementing class in nested, the reference seems perfectly
innocuous. It's not clear whether this is the intended behavior, an
unanticipated edge case, or a bug. So I thought I'd bring it up here.