Odd behavior of object equality/identity in the context of relative vs fully qualified imports

[Nathan Rice]

I just ran into this yesterday, and I am curious if there is a
rational behind it...

I have a class that uses a dictionary to dispatch from other classes
(k) to functions for those classes (v).  I recently ran into a bug
where the dictionary would report that a class which was clearly in
the dictionary's keys was giving a KeyError.  id() produced two
distinct values, which I found to be curious, and
issubclass/isinstance tests also failed.  When I inspected the two
classes, I found that the only difference between the two was the
__module__ variable, which in one case had a name relative to the
current module (foo), and in another case had the fully qualified name
(bar.foo).  When I went ahead and changed the import statement for the
module to import bar.foo rather than import foo, everything worked as
expected.  My first thought was that I had another foo module in an
old version of the bar package somewhere on my pythonpath;  After a
thorough search this proved not to be the case.

Has anyone else run into this?  Is this intended behavior?  If so, why?

Nathan