After switching to nbm-maven-plugin >=4.6, the project no longer builds the cluster correctly. The modules are not added to the cluster anymore.
The copy task uses the same source directory four times with versions >4.6. For each module one execution is performed, including the parent. With version 4.5 it is executed three times only and only for the modules, module-kit, module-a and module-b.

I have set up an example project which shows this issue.
https://github.com/eomasters-repos/cluster-example
In the readme I give more details.

There is a change (aae8671) between 4.5 and 4.6. But I don't know how or if this might cause the issue.