I have very similar symptoms to ones described by Daniel. I'm on up-to-date 12.04, got Minolta PagePro 8L LPT printer also connected to USB via Prolific PL2305 USB<->LPT adapter. The combination was working just fine until I updated from previous LTS to this precise (12.04). Now if I try to print, job appears to queue, then disappears, printer light begins to flash (as if it was receiving/processing data) but nothing else happens. Light flashes seemingly forever and printer status is reported as "Idle - Sending data to printer."

First thing I noticed when I started debugging this was "Filter ... not found." lines in cups error log.  They disappeared after I removed and re-added the printer, but it had no effect on the problem itself.

Following sections "USB printer", "CUPS error_log", and "Capturing print job data" on https://wiki.ubuntu.com/DebuggingPrintingProblems I get.

USB printer
-----------

2)
terotil@pulu:~$ lsmod | grep usb
usblp                  17885  0 
usbhid                 41906  0 
hid                    77367  1 usbhid
usb_storage            39646  1 ums_realtek

3)
terotil@pulu:~$ tail -n 0 -f /var/log/syslog
Nov 18 00:45:43 pulu kernel: [875854.568072] usb 2-1: new full-speed USB device number 7 using uhci_hcd
Nov 18 00:45:43 pulu mtp-probe: checking bus 2, device 7: "/sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1"
Nov 18 00:45:43 pulu mtp-probe: bus: 2, device: 7 was not an MTP device
Nov 18 00:45:43 pulu kernel: [875854.825537] usblp0: USB Bidirectional printer dev 7 if 0 alt 1 proto 2 vid 0x067B pid 0x2305
Nov 18 00:45:43 pulu udev-configure-printer: add /devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1:1.0
Nov 18 00:45:43 pulu udev-configure-printer: device devpath is /devices/pci0000:00/0000:00:1d.0/usb2/2-1
Nov 18 00:45:43 pulu udev-configure-printer: Device vendor/product is 067B:2305
Nov 18 00:45:43 pulu udev-configure-printer: add /devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1:1.0/usb/lp0
Nov 18 00:45:43 pulu udev-configure-printer: failed to claim interface
Nov 18 00:45:43 pulu udev-configure-printer: failed to claim interface
Nov 18 00:45:43 pulu udev-configure-printer: device devpath is /devices/pci0000:00/0000:00:1d.0/usb2/2-1
Nov 18 00:45:43 pulu udev-configure-printer: MFG:Minolta MDL:PagePro 8L SERN:- serial:-
Nov 18 00:45:45 pulu kernel: [875855.989248] usblp0: removed
Nov 18 00:45:45 pulu kernel: [875856.136676] usblp0: USB Bidirectional printer dev 7 if 0 alt 1 proto 2 vid 0x067B pid 0x2305
Nov 18 00:45:45 pulu udev-configure-printer: add /devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1:1.0/usb/lp0
Nov 18 00:45:45 pulu udev-configure-printer: URI matches without serial number: usb://Minolta/PagePro%208L
Nov 18 00:45:45 pulu udev-configure-printer: No serial number URI matches so using those without
Nov 18 00:45:45 pulu udev-configure-printer: device devpath is /devices/pci0000:00/0000:00:1d.0/usb2/2-1
Nov 18 00:45:45 pulu udev-configure-printer: Device already handled
Nov 18 00:45:45 pulu udev-configure-printer: Consider also queues with "/usb/lp0" or "/usblp0" in their URIs as matching
Nov 18 00:45:45 pulu udev-configure-printer: URI of print queue: usb://Minolta/PagePro%208L, normalized: minolta pagepro 8l
Nov 18 00:45:45 pulu udev-configure-printer: URI of detected printer: usb://Minolta/PagePro%208L, normalized: minolta pagepro 8l
Nov 18 00:45:45 pulu udev-configure-printer: Queue ipp://localhost:631/printers/PagePro-8L has matching device URI
Nov 18 00:45:45 pulu udev-configure-printer: Re-enabled printer ipp://localhost:631/printers/PagePro-8L
^C

6)
terotil@pulu:~$ lsusb
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 004: ID 0bda:0158 Realtek Semiconductor Corp. USB 2.0 multicard reader
Bus 002 Device 007: ID 067b:2305 Prolific Technology, Inc. PL2305 Parallel Port
Bus 002 Device 003: ID 04d9:1400 Holtek Semiconductor, Inc. PS/2 keyboard + mouse controller

7)
terotil@pulu:~$ ls -l /dev/usb/lp* /dev/bus/usb/*/*
crw-rw-r-- 1 root root 189,   0 marra  7 21:28 /dev/bus/usb/001/001
crw-rw-r-- 1 root root 189,   3 marra  7 21:28 /dev/bus/usb/001/004
crw-rw-r-- 1 root root 189, 128 marra  7 21:28 /dev/bus/usb/002/001
crw-rw-r-- 1 root root 189, 130 marra  7 21:28 /dev/bus/usb/002/003
crw-rw-r-- 1 root lp   189, 134 marra 18 00:45 /dev/bus/usb/002/007
crw-rw-r-- 1 root root 189, 256 marra  7 21:28 /dev/bus/usb/003/001
crw-rw-r-- 1 root root 189, 384 marra  7 21:28 /dev/bus/usb/004/001
crw-rw---- 1 root lp   180,   0 marra 18 00:45 /dev/usb/lp0

8)
terotil@pulu:~$ sudo usb_printerid /dev/usb/lp0
GET_DEVICE_ID string:
MFG:Minolta;CMD:PrintGear,PCL,PJL;MDL:PagePro 8L;CLS:PRINTER;DES:Minolta PagePro 8L

10)
terotil@pulu:~$ lpinfo -v
direct scsi
direct hp
network smb
network ipp
direct usb://Minolta/PagePro%208L
network socket
network lpd
network http
network beh
network ipps
network ipp14
network https
direct hpfax

CUPS error_log &  Capturing print job data
------------------------

Print job data file was in PDF format and it looked perfectly fine on pdf viewer.

Looks like I can't attach files here, clicking "Add attachment or patch" -link gives 400 bad request. Files are available from http://www.tilus.net/tero/tmp/error_log.txt and http://www.tilus.net/tero/tmp/printout.pdf