Deploying multiple django apps on Apache with mod_wsgi

I want to deploy two different django apps in the same host: The first will correspond to the url /site1 and the second to the url /site2. Here's my configuration:

LoadModule wsgi_module modules/mod_wsgi.so

WSGIScriptAlias /site1 /var/www/py/site1/site1/wsgi.py
WSGIScriptAlias /site2 /var/www/py/site2/site2/wsgi.py

WSGIPythonPath /var/www/py/site1:/var/www/py/site2

<Directory "/var/www/py/site1/site1">
<Files wsgi.py>
Order deny,allow
Allow from all
</Files>
</Directory>

<Directory "/var/www/py/site2/site2">
<Files wsgi.py>
Order deny,allow
Allow from all
</Files>
</Directory>

Also here's the wsgi.py file for both applications

import os
import sys

path = '/var/www/py/site1'
if path not in sys.path:
    sys.path.append(path)

os.environ.setdefault("DJANGO_SETTINGS_MODULE", "site1.settings")
from django.core.wsgi import get_wsgi_application
application = get_wsgi_application()

Now, here's my problem. When I go to my server, let's say http://app1.sites.gr/site1 it some times loads site1, and some other times it loads site2 !!!! The same goes when I visit http://app1.sites.gr/site2 ... Sometiems I get the welcome page for site1, sometimes I get the welcome page for site2 ! I am hitting F5 and getting different welcome pages. I have checked everything for the previous hours and did not find anything strange...

Please, tell me what could be the problem before I go crazy ...

Thanks !