Message 208960 - Python tracker

For a Future f which has already completed, 
  wait( [f,f], return_when=ALL_COMPLETED ) 
blocks forever.

This is because the test in wait():

  if len(done) == len(fs)

is comparing the length of a set to the length of a list. 

If f has not completed, wait( [f,f] ) will yield f once. The behaviour should be consistent with as_completed() - see issue #20367.