Thank you for bringing this to our attention, I have replicated the behavior and the developers are working on a fix now.
In the meantime, you can use the TileDragStarted and TileDragEnded event to persist the tile's opacity. I have written an example application using your code (attached) that demonstrates the workaround.
Thank you for your patience as we work to resolve this issue and thank you for choosing Telerik.
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