Printer incorrect in Win2000 & Citrix

We have a Win2000 network running 3 Citrix XP servers in a farm. This situation doesn't happen all the time and no one particular user. When they logon to a Citrix session the default printer they previously have set is no longer valid. It appears that the default is changed to the defualt of that Citrix server? When you change the default back to their original default that user may work fine for days or maybe the next day it will go back to the default of the Citrix box. Makes no sense. I think it could be a profile problem but do not know what to look for? We are auto creating our printers and have not had any problems with this part. No errors in the log files either? Some of my users have never had the problem and other shave it everyday?? This is frustrating for my users and myself. Help!