Have experienced this problem on 2 win2k pc's on an NT 4.0 network with about 40 PC's, mixed win98, win2k and XP. Problem has only occured on a Dell Optiplex and an IBM Thinkpad when printing to a networked HP4600DN printer. When the PC is powered off and then powered back on, print files from long ago start printing. A search of winnt\system32\spool\printers shows numerous .shd files.
The printer has been reinstalled with the latest drivers and both pc's have all service packs and security patches installed.
A user recently reprinted several hundred full color pages several times because the printer is not visible from her location and was not aware of the printing every time she restarted her PC.