If the user has roaming profiles this may happen due to corruption. That is why deleting the key, logging off and back fixes the issue as the printers get recreated (as the key is now gone).
This article explains the mechanism:
http://support.microsoft.com/kb/102116Some people even go one step further and change a logoff script to get rid of orphaned printers (or all for that user) at logoff by deleting that key so it is recreated fresh every time you logon.
Cláudio Rodrigues
Microsoft MVP - Remote Desktop Services
Citrix CTP