Vista - Using an enum typecoverter in an Excel PIA DLL

I would like to use a TypeCoverter to regionalise output for enums in an
assembly that is a PIA loaded into Excel.

I can run this and it works on an assembly in a test project I created with
an explicitly referenceed assembly, however when running a project that has
been built as an Excel PIA. If I try:
<System.ComponentModel.TypeConverter(GetType(ResourceEnumConverter))> _
public enum MyEnum
ItemA
ItemB
end enum

and in code
myE = MyEnum.ItemA
Dim converter As System.ComponentModel.TypeConverter =
TypeDescriptor.GetConverter(myE)

In the immidiate window
? converter.ToString() goves
"System.ComponentModel.EnumConverter"

whereas in my other project (also a strongly signed assembly, but referenced
directly from a newly created stub windows form project), I get

? converter.ToString
"ClassLibrary1.LocalizedEnumConverter"

so it look like the LocalizedEnumConverter is not being bound to the enum -
any ideas? Is this because of the way Excel loads the assembly, and is there
a way arounfd this?