Using your RadTreeList settings as a reference I have created a sample page, so I could try to replicate the issue, but to no avail.
For your convenience I am attaching the sample page that I have tested on my end. Could you please test the attached page on your side and see if everything is working correctly.
If you continue to experience problems with this, please try to modify the attached sample page in such manner, so it could replicate the problem. Additionally, please elaborate on the exact version that you are using and if possible, attach screenshots with the problematic behavior, so we could get a better idea of the issue.
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