Hello SangGyu,
I tried that with the latest source but the nodes are properly positioned on expanding/collapsing either by code or by hand. I'd suggest you give the official release a try as soon as we announce it. It should be ready and uploaded tomorrow.
You can also send us a sample which shows the problem
via a support ticket (attachments are not allowed in the forums). This way we can test the exact scenario on our end and make sure the problem does not appear anymore.
Best wishes,
Konstantin Petkov
the Telerik team
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