Hello Mikko,
The sample project that I have attached in my reply from March 2, 2020, this duplicate issue is not present.
Please modify the project so that it implements your logic and replicates the issue and send it back to us as an attachment to an official support ticket.
That would allow us to investigate your exact scenario and provide more accurate and specific suggestions.
Regards,
Peter Milchev
Progress Telerik
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