surprising behaviour of os.environ.clear

[Joe P. Cool]

If I call os.environ.clear in a python program child processes still
see the deleted entries. But when I iterate over the keys like so

names =  os.environ.keys
for k in names:
    del  os.environ[k]

then the entries are also deleted for the child processes. Where is
the difference? Is this a bug?
(Observed in Python 2.5.2)

--
Joe