When i use the control on this mode:

this.xmceEntities.SelectedItemsResetButtonVisibility = Visibility.Collapsed;
this.xmceEntities.MultiSelectValueDelimiter = ',';
this.xmceEntities.EmptyText = "Seleccione";
this.xmceEntities.AllowMultipleSelection = true;
this.xmceEntities.DisplayMemberPath = this.DisplayMemberPath;
this.xmceEntities.CheckBoxVisibility = Visibility.Visible;

And i write fast random characters (like monkey typing or biting keyboard) the control throws an exception.

System.InvalidCastException, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</ExceptionType><Message>Invalid cast from 'System.String' to 'System.Nullable`1[[System.Int32, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]'.</Message><StackTrace>   at System.Convert.DefaultToType(IConvertible value, Type targetType, IFormatProvider provider)

at System.String.System.IConvertible.ToType(Type type, IFormatProvider provider)
at System.Convert.ChangeType(Object value, Type conversionType, IFormatProvider provider)
at Infragistics.Controls.Editors.ComboEditorBase`2.AddOrAllowItem(String itemText)
at Infragistics.Controls.Editors.ComboEditorBase`2.ValidateSelection(String text)
at Infragistics.Controls.Editors.ComboEditorBase`2.ProcessEditorText(Boolean allowDropDown, Boolean attemptAutoComplete)
at Infragistics.Controls.Editors.ComboEditorBase`2.ProcessEditorText(Boolean allowDropDown)
at Infragistics.Controls.Editors.ComboEditorBase`2.DelayTracker_Tick(Object sender, EventArgs e)

...