Hello,
It really depends on how your grid is setup for databinding, but I guess that you can take advantage of the IsAsyncPostBack property of WARP - if it is set to true, then we know that we are inside a partial AJAX update and we do not need to rebind the grid (but the actual code depends on how you bind the grid).
More information in IsAsnycPostBack and sample code can be found here:
http://help.infragistics.com/Help/NetAdvantage/NET/2008.2/CLR2.0/html/Infragistics2.WebUI.Misc.v8.2~Infragistics.WebUI.Misc.WebAsyncRefreshPanel~IsAsyncPostBack.html
A very good article on grid databiding in general can be found here:
http://blogs.infragistics.com/blogs/tony_lombardo/archive/2008/01/29/demystifying-infragistics-webgrid-databinding.aspx