Exception in ListFieldIterator on postback

Question

I'm using ListFieldIterator to display/edit values of item from some list. When a postback is triggered (user clicked on button with my custom saving routine), following exception is thrown:

Exception information:

Exception type: NullReferenceException 
Exception message: Object reference not set to an instance of an object. 

Stack trace:    

at Microsoft.SharePoint.WebControls.ListFieldIterator.CreateChildControls()

at System.Web.UI.Control.EnsureChildControls()
at Microsoft.SharePoint.WebControls.TemplateBasedControl.get_Controls()
at System.Web.UI.Control.LoadChildViewStateByIndex(ArrayList childState)
at System.Web.UI.Control.LoadViewStateRecursive(Object savedState)
at System.Web.UI.Control.LoadChildViewStateByIndex(ArrayList childState)
at System.Web.UI.Control.LoadViewStateRecursive(Object savedState)
at System.Web.UI.Control.LoadChildViewStateByIndex(ArrayList childState)
at System.Web.UI.Control.LoadViewStateRecursive(Object savedState)
at System.Web.UI.Control.LoadChildViewStateByIndex(ArrayList childState)
at System.Web.UI.Control.LoadViewStateRecursive(Object savedState)
at System.Web.UI.Control.LoadChildViewStateByIndex(ArrayList childState)
at System.Web.UI.Control.LoadViewStateRecursive(Object savedState)
at System.Web.UI.Control.LoadChildViewStateByIndex(ArrayList childState)
at System.Web.UI.Control.LoadViewStateRecursive(Object savedState)
at System.Web.UI.Control.LoadChildViewStateByIndex(ArrayList childState)
at System.Web.UI.Control.LoadViewStateRecursive(Object savedState)
at System.Web.UI.Page.LoadAllState()
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

Displayed list doesn't contain any custom fields that could be the cause of exception.