I found the answer!
Instead of including JS files through ClientScript.RegisterClientScriptInclude, they should be added to ScriptManager as ScriptReference elements through markup or code.
, javascript "JScript1.js", ScriptManager, ():
<Scripts>
<asp:ScriptReference Path="~/JScript1.js" />
</Scripts>
</asp:ScriptManager>
():
ScriptManager1.Scripts.Add(new ScriptReference("~/JScript1.js"));