@Ceki Gulcu, now I understand that this is not an issue for logback, but current implementation is not predictable unfortunately.
ch.qos.logback.core.joran.util.beans.BeanDescriptionFactory creates BeanDescription based on output of

Method[] methods = clazz.getMethods();  // Line 32

And according to java documentation:

The elements in the returned array are not sorted and are not in any particular order.

So, BeanDescription could be as:

{nestedField=public void ClassA.addNestedField(java.lang.String)}
// or
{nestedField=public void ClassB.addNestedField(java.lang.Integer)}

Maybe it makes sense to implement ch.qos.logback.core.joran.util.beans.BeanDescriptionFactory#create with predictable output.
What do you think? (For example as I proposed to take method definition from leaf element of classes hierarchy or only from parent one and ignore leaves)