Just a quick post today. I was troubleshooting an issue where a user would set a default network printer (say Printer01) in their user profile, upon a server restart (which happens nightly) their printer would be set back to the Adobe PDF local printer. After going through event logs and some basic troubleshooting through Group Policy I quickly came to the conclusion that this was more of a user profile issue than a deployment one.
After a bit of Google-foo, I found that Windows stored user based printer connection details in the registry under HKEY_USERS\<user SID here>\Printers\Connections. It also stored local settings for each printer under HKEY_USERS\<user SID here>\Printers\Settings. I went through the printer keys under each registry key and found printers that no longer existed.
Simply deleting printers that were no longer available let the user set a default printer and the setting stayed after a server or print spooler service reboot.