Ajax - Gridview Paging Doesn’t Work Inside UpdatePanel

Altough questions somehow similar to this have been asked for a number of times, but the question is still unsolved. Here is the question: I have a gridview which is contained in a tab container ajax control which itself is inside an updatepanel. Gridview works excellent and its corresponding methods are fired accurately, but when I enable paging, (e.g.) after I click on page 2, the gridview hides itself. here is my PageIndexChanging method:

protected void GridView1_PageIndexChanging(object sender, GridViewPageEventArgs e)
{
GridView1.PageIndex = e.NewPageIndex;
GridView1.DataBind();
UpdatePanel2.Update();
}

Why paging causes gridview to stop working correctly? What can I do?