I have a SL 4 app with Infrigistics 2011 to use XamComboEditor in following way:

xaml is:

<ig:XamComboEditor
IsEditable="False" ItemsSource="{Binding MyList}" CheckBoxVisibility="Collapsed"
SelectedItem="{Binding MyItem, Mode=TwoWay,FallbackValue='='}"
AllowMultipleSelection="False">
</ig:XamComboEditor>

data binding for this XamComboEditor is:

List<string> MyList = new List<string>();
MyList.Add("= ");
MyList.Add("!=");
MyList.Add("<=");
MyList.Add(">=");
MyList.Add("<");
MyList.Add(">");

when run the app, it is fine, users can see the operators in dropdown like:
=
!=
<=
>=
<
>

but after upgrade this app to SL5 with Infrisgistics 2012, the display for the dropdown become:
2
2
2
2
1
1

not sure why. How to fix it quicky?