Suddenly, ModelDoc2::GetPathName() has decided to alter the path ever so slightly in some code I have written.  Everything was working fine when suddenly, my EPDM add-in started exhibiting unexpected behavior.  I finally tracked it down to a simple method I wrote to get the ModelDoc2 for an EPDM file that is open in SolidWorks:

 /// 
 /// Retrieves the SOLIDWORKS ModelDoc2 object for an EPDM file open in SOLIDWORKS.
 /// Open files do not have to be visible in their own window.  Any referenced file
 /// that is not suppressed or lightweight is an open file
 /// 
 /// the EPDM file
 /// null, if SOLIDWORKS is not running or the specified document is not open.
 /// Otherwise, it returns the ModelDoc2 object associated with the file.
 public static ModelDoc2 getOpenSolidWorksDocument(IEdmFile11 file)
 {
     if (!solidworksIsRunning())
     {
         return null;
     }
     object openDocs = getSolidWorks().GetDocuments();
     if (openDocs == null)
     {
         return null;
     }
     foreach (object nextDocObj in (object[])openDocs)
     {
         ModelDoc2 nextDoc = (ModelDoc2)nextDocObj;
         if (nextDoc.GetPathName().Equals(file.GetLocalPath(Utilities.getFileFolder(file).ID)))
         {
             return nextDoc;
         }
     }
     return null;
 }

The method was returning 'null' even though I was certain that the file was open in SOLIDWORKS.  I set a breakpoint in the code and then used the Immediate window to see what was going on:

The value returned by nextDoc.GetPathName() was

"C:\\_2016SP0\\Engineering\\Projects\\123456-TES PROJECT\\4. Mechanical WIP\\ASSY RELEASE TESt\\C.SLDASM"

and the value returned by file.GetLocalPath(Utilities.getFileFolder(file).ID) was

"C:\\_2016SP0\\Engineering\\Projects\\123456-TES PROJECT\\4. Mechanical WIP\\ASSY RELEASE TEST\\C.SLDASM"

It took me a couple of minutes to spot the problem.  For some reason, GetPathName() decided to change the upper case T to lower case for the ASSY RELEASE TEST folder.  This folder is not now, nor has it even been  ASSY RELEASE TESt.

The fix is simple.  I just change the comparison to this:

(nextDoc.GetPathName().Equals(file.GetLocalPath(Utilities.getFileFolder(file).ID),StringComparison.OrdinalIgnoreCase)

but the mind boggles as to why it would happen in the first place.