Delete list item - Security validation becomes invalid (no code solution)

I have a sharepoint list with no code/event recievers behind. When I try to delete an item using the item dropdown menu I get "The security validation for this page is invalid.Click Back in your Web browser, refresh the page, and try your operation again". But deleting using the delete button in ribbon or in the edit item popup windows works just fine.

We have the <asp:FormDisgest> control in our master page.

The only special thing about this site that we are using FBA authentication, also I have two web applications using the same content database (extend web application).

Setting security validation=off do work but I guess that is a major security risk.

We are using SharePoint 2010 SP1.