Generally rebind() method will request the server (post-back or ajax request if the grid is ajaxified). The second rebind may not be able to reach the server. Such approach will be successful only if the grid data-binding is asynchronous - for example client-side data-binding.
I suggest you to ajaxify your grids with RadAjaxManager and perform the required update as below:
"<%= RadAjaxManager.GetCurrent(Page).ClientID %>"
In server side RadAjaxManager1_AjaxRequest
sender, Telerik.Web.UI.AjaxRequestEventArgs e)
Thus you can rebind the grids in one call back.
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