Please try the following hotfix first.
972600 The default printer setting is changed on the console after you disconnect a remote desktop session from a Windows Vista or a Windows Server 2008-based terminal server
http://support.microsoft.com/default.aspx?scid=kb;EN-US;972600If the issue persists, let us know how did you configure the network printer. Did you deploy them via Group Policy or Logon script?
If you use Group Policy to deploy printers, as a workaround, you can refer to the following article to configure default printer:
How to Add a Default Printer Using a Visual Basic Script
http://support.microsoft.com/kb/263226 if you are open up citrix presentation server console, go to policies, click on default policy..go to 'printing' menu on the left side, then expand the hierachy, go to 'session printers'...i think under 'choose client's default printer' select 'set default printer to the client's main printer'.
Thanks.