Hi,
I have a line of code that throws an ArgumentNullException.
When this line executes it behaves as if the exception was caught somewhere and silently 'swallowed' - i.e the app continues running

But I don't have any exception handlers that would catch this and if I set the debugger to break when the exception is thrown (rather than just when unhandled) and then continue to step through the code no other code executes and the app continues to run (but stepping kicks in again say for a mousemove event....)

Any clues as to what can cause this behaviour?
TIA,
Viv

UPDATE: I get this in the Output window when I continue after the error (code is triggered by an OnDrop():

Step into: Stepping over non-user code 'System.Windows.RoutedEventArgs.InvokeHandler'
Step into: Stepping over non-user code 'System.Windows.UIElement.RaiseEventImpl'
Step into: Stepping over non-user code 'System.Windows.ReverseInheritProperty.FirePropertyChangeInAncestry'
Step into: Stepping over non-user code 'System.Windows.ReverseInheritProperty.OnOriginValueChanged'
Step into: Stepping over non-user code 'System.Windows.Input.MouseDevice.ChangeMouseOver'
Step into: Stepping over non-user code 'System.Windows.Input.MouseDevice.PreProcessInput'
Step into: Stepping over non-user code 'System.Windows.Input.InputManager.ProcessStagingArea'
Step into: Stepping over non-user code 'System.Windows.Input.InputProviderSite.ReportInput'
Step into: Stepping over non-user code 'System.Windows.Interop.HwndMouseInputProvider.ReportInput'
Step into: Stepping over non-user code 'System.Windows.Interop.HwndMouseInputProvider.FilterMessage'
Step into: Stepping over non-user code 'System.Windows.Interop.HwndSource.InputFilterMessage'
Step into: Stepping over non-user code 'MS.Win32.HwndWrapper.WndProc'
Step into: Stepping over non-user code 'MS.Win32.HwndSubclass.DispatcherCallbackOperation'
Step into: Stepping over non-user code 'System.Windows.Threading.ExceptionWrapper.InternalRealCall'
Step into: Stepping over non-user code 'System.Windows.Threading.ExceptionWrapper.TryCatchWhen'
Step into: Stepping over non-user code 'System.Windows.Threading.Dispatcher.InvokeImpl'
Step into: Stepping over non-user code 'MS.Win32.HwndSubclass.SubclassWndProc'
Step into: Stepping over non-user code 'System.Windows.Threading.Dispatcher.PushFrameImpl'

Only thing I can think of is that something is swallowing it in there......