This older post 
http://bytes.com/groups/python/786579-python-2-2-1-select
describes a similar problem where select() is used on a buffered file
object (a pipe to another process)

IMO it should be documented that select() does not work so well for
objects which have a fileno(), but do data buffering: select() only sees
the file descriptor and cannot know whether there is data in the buffer.