Correct me if I am wrong, but I believe that you are docking / undocking the sliding pane on the server. You can observe this behavior if you are not setting the size of the panes affected by the docking functionality. Please find attached a sample page demonstrating the correct approach to dock / undock sliding pane server-side.
If this is not the case, could you please provide the exact configuration of RadSplitter and the code implementing the programmatic "open and close" functionality?
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