Some network printers are configured to demand credentials (username and password) for every print job. When setting up a printer using the system-config-printer-kde component, these credentials can be entered.
Once the required credentials change, printing with the old settings leads to unexpected behavior (the print job is processed as usual, is locally completed and removed from the print queue) and simply doesn't appear on the printer.

reproduce:
- set up a printer that demands a username + password
- configure that printer with the required username + password combination and ensure printing works as expected
- change the required credentials on the printer and print again

expected:
- any kind of hint that the job couldn't be processed (best that the credentials were wrong)
- ideally a dialog allowing to enter the updated credentials

actual:
- the job is removed from the print queue the same way that successfully printed jobs do; this makes it very hard to guess why the actual printing never happens

note:
It is not unusual that employers and universities require changing passwords on a regular basis. Since such credentials are usually shared, the print system is also affected. However, as changing the credentials and printing do frequently not happen in a small time frame (eg. sending the first print job a week or two after updating the credentials), it is not straight forward to understand the root of the problem (eg. the printer doesn't print). It would be highly useful if a notification could help the user understand the problem and in the best case possible allow them to update their password.