Github user pmouawad commented on the issue:
https://github.com/apache/jmeter/pull/300
It seems the creation order is important to reproduce:
First create Thread Group 1, add to it a Debug Sampler1
Second create Thread Group 2, add to it a Debug Sampler2
Add User Defined Variables, move it before Thread Group 1
Unfold TG2 and fold TG1
Duplicate User Defined Variables
Play with undo, redo it is broken, it seems the element moving is not
correctly handled.
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