Do macro-enabled Word 2010.docm files, defeat Co-Authoring?

[Outerspace Visitor]

We rolled out a macro-enabled Word 2010 .docm into Sharepoint and found that the first user to edit it, causes all others to get "Locked for Editing By Another User".

But if we save the .doc. as a .doc, co-authoring is possible.

We wonder if having a macro in a .docm indeed causes co-authoring to fail, or maybe it's some other phenomenon.

The macro in question is very simple, just a config to adjust some Word settings when a user opens the .docm:

Sub AutoOpen()
' AutoOpen Macro
' macro to display bookmarks, field shading, formatting marks, _
table grid lines and turn off Track Formatting in Track Changes _
on opening an existing document based on the template

With ActiveWindow.View
.ShowAll = True
.ShowBookmarks = True
.FieldShading = wdFieldShadingAlways
If ActiveDocument.ActiveWindow.View.TableGridlines = False Then
ActiveDocument.ActiveWindow.View.TableGridlines = True
End If
End With

With ActiveDocument
.TrackFormatting = False
End With

End Sub

[Outerspace Visitor]

To answer my own question, Sharepoint 2010 does not support Word co-authoring for anything other than .docx documents.