Hi Billy Hasan,
Thank you for clarifying this.
This behavior is normal when you do not have Load On Demand enabled and the RadComboBox is read-only. After postback, the RCB has only one Item - the default one as it is loaded from ViewState (LOD Items are not persisted across postbacks), so its Text and Value are the actual ones, so the selection made on the client is lost.
You can work around this if you disable the ViewState of the RCB, enable its AllowCustomText property and make the control read-only on the client:
Then you have to add the Default Item on each postback and pre-select it only on the first page load:
Please let me know if this setup is useful to you.
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