AutoCompleteBox causes an ArgumentException when setting ItemFilter delegate through XAML

[tatoadsl]

AutoCompleteBox causes an ArgumentException when setting ItemFilter delegate through XAML. The exception is thrown when go through the InitializeComponent method indicating the "Type must derive from delegate".

Setting the XAML for the AutoCompleteBox with the properties:
ItemFilter="SearchMethod"
FilterMode="Custom"

SearchMethod is implemented in the codebehind as;

public bool SearchMethod(string searchText, object item)

The exception is thrown yet the methos is set up and working.