Overlapping detection inconsistent?

[Ir3nicuz]

I use LibGdx and the Bullet Java Wrapper. I play around with the possibilities of the "btGhostObject" class to detect overlapping shapes in a 3D physics environment. I came up to a strange behaviour which I not understand. The dispatcher keeps correctly track of all overlapping objects, but the "OverlappingObjects" data structure within the "btGhostObject" is constantly "0" at any given call within the "ContactListener" callbacks.

I cannot say if this is a basic understanding issue or a bug/timing issue of the Bullet Java Wrapper. But since LibGdx-Bullet has no discussion forum this is the only place to ask. :)

I give my "btGhostObject" the UserValue "2" as ID. I set the collision group and collision mask like mentioned in the documentation as "cross over" (objectA group to objectB mask and vice versa).

This is the log result of polling the dispatcher manifolds in the render calls and the ContactListener callbacks at occurance:
log.txt
The dispatcher manifolds correctly detect the overlap start at "2025-05-11T11:08:58.676510200" and the end at "2025-05-11T11:09:00.756343500". But all the callbacks "onContactStarted" and "onContactEnded" in between gave "0"overlapping objects in the btGhostObject's data structure with Id "2".

It looks to me the "OverlappingObject" data structure in the btGhostobject is never filled or used.
Is this intended? Or the wrong attempt to get the overlapping object count in the callbacks?