MEF: ErrorTag: how to get the ErrorTag ToolTipContent to work in VS2010 extensibility component

Environmental details:

Microsoft Visual Studio 2010 Version 10.0.40219.1 SP1Rel 

Microsoft .NET Framework Version 4.5.51641 SP1Rel

Installed Version: Professional

Microsoft Visual Basic 2010   01018-532-2002102-70585
Microsoft Visual Basic 2010

Problem:

I have made a MEF extension that implements an ErrorTag/Margin Glyph combination and everything is working except that I cannot get the ErrorTag's tooltip to display. I do see the relevant "squiggle" so I know the tag is working in that sense.

My class code for the Tag is written in VB.net :

Friend Class CodeSmellTag
    Inherits ErrorTag
    Implements IGlyphTag ', IErrorTag

    Private m_TagType As CodeSmellTagType

    Public Sub New(TagType As CodeSmellTagType)
        MyBase.New("compiler warning", "Test Tool Tip")
        m_TagType = TagType
    End Sub

    Public ReadOnly Property TagType As CodeSmellTagType
        Get
            Return m_TagType
        End Get
    End Property

End Class

Does anyone have any experience with ErrorTags and tooltips that might help?