Why does ObjectDBX.AxDBDocument not release file lock if I add an object to the DWG file?

Question

I have a python program that I am developing using RevitPythonShell and one task that it does is to establish a COM link to an Autocad file using the ObjectDBX.AxDBDocument interface. The program will then read the database for various graphical entities and may, depending on the file's content, create or delete entities in that file.

To handle the COM access to Autocad, I have created a Python class with __exit__ and __enter__ functions that when used with Python's with structure will automatically upon exit, close the DWG file and takedown the COM link.

This works as expected except when I added one particular function to my program - when that function is active, the program will proceed without error but DWG is locked even though the program has finished execution. That is, the program is done but trying to open the DWG file with Autocad gives a "Open File as read-only?" message. To release the lock, I have to completely shut down Revit. Shutting down RevitPythonShell is not enough.

Here is the offending function:

def CreateAttributeReplacements (BlkRef, MSpace):
  #MSpace = BlkRef.Document.ModelSpace
  Attr = BlkRef.GetAttributes()
  CAttr = BlkRef.GetConstantAttributes()

  Layer = BlkRef.Layer
  LineType = BlkRef.Linetype
  LTScale = BlkRef.LinetypeScale
  Color = BlkRef.TrueColor

  Rst = []

  #return Rst  ----> if I short-circuit function here, things work as expected.
  
  print "CreateAttr"
  for item in Attr:
    if item.MTextAttribute:
      temp = MSpace.AddMText (item.InsertionPoint, item.MTextBoundaryWidth, item.MTextAttributeContent)
      temp.DrawingDirection = item.MTextDrawingDirection
      temp.Height = item.Height
    else:
      temp = MSpace.AddText (item.TextString, item.InsertionPoint, item.Height)
      temp.Alignment = item.Alignment
      temp.Backward = item.Backward
      temp.ScaleFactor = item.ScaleFactor
      #temp.TextGenerationFlag = item.TextGenerationFlag #should work but does not.
      temp.UpsideDown = item.UpsideDown
      temp.ObliqueAngle = item.ObliqueAngle #Should work but does not.

    #Common properties
    temp.Layer = Layer
    temp.Linetype = LineType
    temp.LinetypeScale = LTScale
    temp.TrueColor = Color
    temp.StyleName = item.StyleName
    
    Rst.append (temp)
    temp = None
  return Rst

The problem seems to have something to do with the Add.Text and Add.MText part of the function. If I short-circuit the function with a return statement at the place shown, the problem goes away.

Alternately, if I do not short-circuit the function but instead open a second file - which automatically closes the first file - the problem goes away.

So, does anyone know what I might be doing wrong? Or has anyone seen this problem before? Is it a bug?

Sincerely; Michelle

PS: I am using Revit 2019 and Autocad 2022 (office) or Revit 2019 and Autocad 2016 (home)