Balsam seems to interpret a sphere parented under leaf joint as joint

The attached fbx file contains a cylinder, deformed by an animated skeleton hierarchy.
A sphere is parented under the leaf joint.

When running balsam on the file then there is only one mesh created (for the cylinder).
Looking in the .qml file I can see that the sphere is interpreted as a joint

Skeleton {
id: qmlskeleton
Joint {
id: joint1
...
Joint

}