Python 3.7 (2.7 looks almost the same):

class Demo(builtins.object)
 |  Data descriptors defined here:
 |  
 |  __dict__
 |      dictionary for instance variables (if defined)
 |  
 |  __weakref__
 |      list of weak references to the object (if defined)
 |  
 |  data
 |      Doc of a data-descriptor.
 |  
 |  non_data
 |      Doc of a non-data descriptor.
 |  
 |  prop
 |      Doc of a property.

Python 3.8:

class Demo(builtins.object)
 |  Readonly properties defined here:
 |  
 |  data
 |      Doc of a data-descriptor.
 |  
 |  non_data
 |      Doc of a non-data descriptor.
 |  
 |  prop
 |      Doc of a property.
 |  
 |  ----------------------------------------------------------------------
 |  Data descriptors defined here:
 |  
 |  __dict__
 |      dictionary for instance variables (if defined)
 |  
 |  __weakref__
 |      list of weak references to the object (if defined)

Python 3.9:

class Demo(builtins.object)
 |  Readonly properties defined here:
 |  
 |  data
 |  
 |  non_data
 |  
 |  prop
 |      Doc of a property.
 |  
 |  ----------------------------------------------------------------------
 |  Data descriptors defined here:
 |  
 |  __dict__
 |      dictionary for instance variables (if defined)
 |  
 |  __weakref__
 |      list of weak references to the object (if defined)

Seems the original bug was fixed, but a regression was introduced in 3.9.