Apache2 unexcepted behavior log file

Question

Since today, error log from apache stop writting in the path i've given, instead it goes back in the default logging file.

I the apache2 vhost config, i've set the ErrorLog to a value

${APACHE_LOG_DIR}/ghost_error.log ,

but when there is error to log, it's write in the

${APACHE_LOG_DIR}/error.log

We are using Flask with apache2.

There is the config file for apache2

<VirtualHost *:80>
[...]
ServerAdmin webmaster@localhost
WSGIScriptAlias / /var/www/ghost/ghost.wsgi

[...]

ErrorLog ${APACHE_LOG_DIR}/ghost_error.log
CustomLog ${APACHE_LOG_DIR}/ghost_access.log combined
</VirtualHost>

And there is the wsgi file:

#!/usr/bin/python
try:
  ghost_path='/home/www'
  chdir_this = '%s/ghost/' % ghost_path
  activate_this = '%s/ghost_env/bin/activate_this.py' % ghost_path
  import os
  os.chdir(chdir_this)
  execfile(activate_this, dict(__file__=activate_this))

  reload(os)
  import sys
  import logging

  os.chdir(os.path.abspath(os.path.dirname(__file__) + "/App/"))
  sys.path.insert(0, os.path.abspath(os.path.dirname(__file__) + "/App/"))
  sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
  from App import app as application
except Exception, e:
  import traceback
  with open('/tmp/ghost.fail.log', 'w') as f:
    f.write("%s\n%s" % (e, traceback.format_exc()))

We simply have no idea of where it can come from. If you do have some hint to follow !

Thanks.