SymbolTreeInfo is ignoring extension method from VB compiled PE reference

[genlu]

Here's the code that builds SymbolTreeInfo for metadata:
http://source.roslyn.io/#Microsoft.CodeAnalysis.Workspaces/FindSymbols/SymbolTree/SymbolTreeInfo_Metadata.cs,393

The problem is the IL for module contains extension methods in VB looks like this (i.e. sealed but not abstract):

One issue this causes is "add using" won't be able to fix a reference to extension method declared in such a metadata reference.