[python-win32] Error 1789 during logon, except not really called

[le dahut]

Hello,

I'm using this code :
     mypdc = 'mypdc'
     dusers = 'DomName\DomainUsers'
     obj = 'C:\\Mylogfile.log'
     try:
         domainusers_sid = wsec.LookupAccountName(mypdc, dusers)[0]
         info = wsec.DACL_SECURITY_INFORMATION
         sd = wsec.GetFileSecurity(obj, info)
         acl = sd.GetSecurityDescriptorDacl()
         acl.AddAccessAllowedAceEx(wsec.ACL_REVISION_DS, 
wsec.OBJECT_INHERIT_ACE, wf.FILE_ALL_ACCESS, domainusers_sid)
         # maj du Security Descriptor
         sd.SetSecurityDescriptorDacl(1, acl, 0)
         # application sur l'objet
         wsec.SetFileSecurity(obj, info, sd)
     except Exception, e:
         logging.error("ACLs error %s"%([obj, dusers, e]))
         logging.debug('Error %s'%traceback.print_exc())

At logon time, it can occur that wsec.LookupAccountName fails. The 
except statement is called but an exception is thrown as well and I get 
a file logon.exe.log in which I can read the traceback. And finally 
traceback.print_exc() returns None.

Why does this produce a traceback instead of really except it ?