I'll demonstrate the problem:
Consider the following package hierarchy:
  
  p/
    __all__.py
    m1.py
    m2.py

The contents of m1 and m2 modules are:
-----m1.py----
import m2
import p.m2
--------------

-----m2.py----
print 'Loading m2 module'
--------------

Running the m1 module would yield the output
  Loading m2 module
  Loading m2 module
. As it is obvious from the output the module m2 is
loaded twice. The problem arrises when you want to do
things such as implementing a singleton class:

-----Alternate m2.py-----
class Singleton(object):
  _instance = None
  @staticmethod
  def getInstance():
    if Singleton._instance is None:
      Singleton._instance = Singleton()
    return _instace
-------------------------

-----Alternate m1.py-----
import m2
import p.m2

print m2.Singleton.getInstance()
print p.m2.Singleton.getInstance()
-------------------------

If you run m1 module, the output shows that the two
instaces are not the same objects. That is m2.Singleton
and p.m2.Singleton are not the same classes. 

I think this is a bug.

Logged In: YES 
user_id=21627

At first, I could reproduce the problem; look at this
transcript to see what I did.

martin@mira:~/tmp$ mkdir p
martin@mira:~/tmp$ echo >p/__init__.py
martin@mira:~/tmp$ cat >p/m1.py
import m2
import p.m2
martin@mira:~/tmp$ cat >p/m2.py
print 'Loading m2 module'
martin@mira:~/tmp$ python
Python 2.3.5 (#2, Mar  6 2006, 10:12:24)
[GCC 4.0.3 20060304 (prerelease) (Debian 4.0.2-10)] on linux2
Type "help", "copyright", "credits" or "license" for more
information.
py> import p.m1
Loading m2 module
py>

As you can see, the "Loading" output is printed only once.

This might happen if you run p/m1.py as the main program,
but I cannot reproduce it:

martin@mira:~/tmp$ python p/m1.py
Loading m2 module
Traceback (most recent call last):
  File "p/m1.py", line 2, in ?
    import p.m2
ImportError: No module named p.m2

As the current directory is not on sys.path, it won't find
the package p.

Now, if you also change that (e.g. by setting PYTHONPATH), I get

martin@mira:~/tmp$ export PYTHONPATH=`pwd`
martin@mira:~/tmp$ python p/m1.py
Loading m2 module
Loading m2 module

This is not a bug: Now *both* the current directory, and the
directory ~/tmp/p are on sys.path (print sys.path inside m1
to see what I mean).

When you do "import m2", it searches for a module named m2
on sys.path, and it finds p/m2.py. When you then import
p.m2, it searches for a package p on sys.path, finds the
package, and then imports the module m2. It happens that
both modules have the same source file - yet they are
different modules.

If you change the print statement to

print 'Loading', __name__, 'module'

you get

Loading m2 module
Loading p.m2 module

So in short: this is not a bug. Don't try running a module
in a package as the main program.