WPF: NullReferenceException at Automation.Peers.ItemAutomationPeer.GetNameCore

I have a vexed problem and have spent a whole day for it, but still can't fix it. I have a button on WPF UI,it is used to add a item to treeview, the code in xaml is below:

<Button Content="Create Item"  
                                        Command="{Binding NewItem}"
                                        Click="NewItemButton_Click"
                                        TabIndex="16"                                                                                           
                                        ToolTip="{Binding NewItemHelpText}"
                                        ToolTipService.ShowOnDisabled="True">
                                        <Button.IsEnabled>
                                            <MultiBinding Converter="{StaticResource LogicalAndConverter}">
                                                <Binding Path="CurrentItem" Converter="{StaticResource ItemCreationConverter}"/>
                                                <Binding Path="ControlMode" Converter="{StaticResource MyConverter}" ConverterParameter="{x:Static local:Option.ReadOnly}"/>
                                            </MultiBinding>
                                        </Button.IsEnabled>
                                    </Button>

Sometimes, after click this button, will throw a exception,

> ERROR MyApplication.App [(null)] - Error in MyApplication
   System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Windows.Automation.Peers.ItemAutomationPeer.GetNameCore()
   at System.Windows.Automation.Peers.AutomationPeer.UpdateSubtree()
   at System.Windows.Automation.Peers.AutomationPeer.UpdateSubtree()
   at System.Windows.Automation.Peers.AutomationPeer.UpdateSubtree()
   at System.Windows.Automation.Peers.AutomationPeer.UpdatePeer(Object arg)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)

this exception throwed randomly, after add some log to debug the code, I find that both NewItemButton_Click event and NewItem command execute to the end, I search my work solution, didn't find anything about Automation, I don't know why and where this exception throwed.

Can somebody help me? thanks.