Why would TLB generated from C# assembly lowercase the leading character of some property names?

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VS2013

This is odd:
I have an interface in C#:

C#

[ComVisible(true)]
[Guid("24BDD90E-373B-400F-B374-1350CDB9FE76")]
[InterfaceType(ComInterfaceType.InterfaceIsDual)]
public interface IGURecord
{
  [DispId(1)]
  string Id { get; }
  [DispId(2)]
  double GUValue { get; }
  [DispId(3)]
  double RelativeMigrationTime { get; }
  [DispId(4)]
  string GlycanName { get; }
  [DispId(5)]
  double MonoisotopicMass { get; }
}

In the generated .TLB the GUValue, RelativeMigrationTime and GlycanName properties are getting the leading characters lowercased:

interface IGURecord : IDispatch {
    [id(0x00000001), propget]
    HRESULT Id([out, retval] BSTR* pRetVal);
    [id(0x00000002), propget]
    HRESULT guValue([out, retval] double* pRetVal);
    [id(0x00000003), propget]
    HRESULT relativeMigrationTime([out, retval] double* pRetVal);
    [id(0x00000004), propget]
    HRESULT glycanName([out, retval] BSTR* pRetVal);
    [id(0x00000005), propget]
    HRESULT MonoisotopicMass([out, retval] double* pRetVal);
};

Does anyone have any ideas on why this could be happening?

What I have tried:

There isn't anything unusual I'm doing in this C# assembly.
This is VS 2013.
I've checked the "Register for COM interop" in the project build settings.
There are other interfaces in this assembly defined similarly that aren't seeing this issue.

Posted 14-Jul-16 11:22am

Matt T Heffron

Updated 15-Jul-16 12:26pm

v2

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Matt T Heffron · Accepted Answer · 2016-07-15T12:26:00

OK, I'm going to claim this is a bug, although I don't know if it's in Visual Studio, or in REGASM.exe when it creates the Type library:

It seems that somewhere along the process identifiers are not being considered totally unique based on casing. I had methods on the other ComVisible interfaces that had parameters that used the same identifiers that were the problems here, except with the leading lowercase.
I also noticed something else: I had parameters on some methods that were cased the same as different property names.

On a hunch, I renamed all of the method property names so that they didn't match any identifiers with different casing.
That solved the issue.
All of the identifiers in the Type Library now have the same casing as in the defining C# interfaces.