Duplicate copies embedded elements twice when expanded

@FSchumacher ([Bug 62299](https://bz.apache.org/bugzilla//show_bug.cgi?id=62299&redirect=false)):
When duplicating an element with exapanded children like the following element structure:

+ Sampler A
- Child A
Sampler B

Duplicating the structure will result in

+ Sampler A
- Child A
Sampler B
+ Sampler A
- Child A <--- (this will actually not be expanded)
Child A <--- (this is an unexpected copy and on the wrong level)
Sampler B

Severity: normal
OS: Linux