a further update/upgrade in apt-get got me the remainder of the ppa8 files. Tests as below (NOT the ppa9 which was mentioned in the latest request of comment 83):

$ lpstat -v
device for ML-4500: usb://Samsung/ML-4500

$ sudo /usr/lib/cups/backend/usb
DEBUG: list_devices
DEBUG: libusb_get_device_list=13
DEBUG: Printer found with device ID: MFG:Samsung;CMD:GDI;MDL:ML-4500;CLS:PRINTER;MODE:GDI;STATUS:IDLE; Device URI: usb://Samsung/ML-4500
direct usb://Samsung/ML-4500 "Samsung ML-4500" "Samsung ML-4500" "MFG:Samsung;CMD:GDI;MDL:ML-4500;CLS:PRINTER;MODE:GDI;STATUS:IDLE;" ""

$ sudo /usr/lib/cups/backend/usb
DEBUG: list_devices
DEBUG: libusb_get_device_list=13
DEBUG: Printer found with device ID: MFG:Samsung;CMD:GDI;MDL:ML-4500;CLS:PRINTER;MODE:GDI;STATUS:IDLE; Device URI: usb://Samsung/ML-4500
direct usb://Samsung/ML-4500 "Samsung ML-4500" "Samsung ML-4500" "MFG:Samsung;CMD:GDI;MDL:ML-4500;CLS:PRINTER;MODE:GDI;STATUS:IDLE;" ""

[power cycle]

$ sudo /usr/lib/cups/backend/usb
DEBUG: list_devices
DEBUG: libusb_get_device_list=13
DEBUG: Printer found with device ID: MFG:Samsung;CMD:GDI;MDL:ML-4500;CLS:PRINTER;MODE:GDI;STATUS:IDLE; Device URI: usb://Samsung/ML-4500
direct usb://Samsung/ML-4500 "Samsung ML-4500" "Samsung ML-4500" "MFG:Samsung;CMD:GDI;MDL:ML-4500;CLS:PRINTER;MODE:GDI;STATUS:IDLE;" ""

[print job 10 - no printout]

$ cancel -a
$ sudo /usr/lib/cups/backend/usb
DEBUG: list_devices
DEBUG: libusb_get_device_list=13
DEBUG: Printer found with device ID:  Device URI: usb://Unknown/Printer
direct usb://Unknown/Printer "Unknown" "Unknown" "" ""
DEBUG: Failed to set configuration 1 for 067b:2305

[power cycle]

$ lpstat -v
device for ML-4500: usb://Samsung/ML-4500

$ lsusb
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 006 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 007 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 008 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 009 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 004 Device 002: ID 04f2:0402 Chicony Electronics Co., Ltd Genius LuxeMate i200 Keyboard
Bus 004 Device 013: ID 067b:2305 Prolific Technology, Inc. PL2305 Parallel Port
Bus 004 Device 004: ID 050d:0119 Belkin Components F5U120-PC Dual PS/2 Ports / F5U118-UNV ADB Adapter
Bus 002 Device 002: ID 152d:2339 JMicron Technology Corp. / JMicron USA Technology Corp. JM20339 SATA Bridge

$ sudo /usr/lib/cups/backend/usbDEBUG: list_devices
DEBUG: libusb_get_device_list=13
DEBUG: Printer found with device ID: MFG:Samsung;CMD:GDI;MDL:ML-4500;CLS:PRINTER;MODE:GDI;STATUS:IDLE; Device URI: usb://Samsung/ML-4500
direct usb://Samsung/ML-4500 "Samsung ML-4500" "Samsung ML-4500" "MFG:Samsung;CMD:GDI;MDL:ML-4500;CLS:PRINTER;MODE:GDI;STATUS:IDLE;" ""

$ lsusb
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 006 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 007 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 008 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 009 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 004 Device 002: ID 04f2:0402 Chicony Electronics Co., Ltd Genius LuxeMate i200 Keyboard
Bus 004 Device 013: ID 067b:2305 Prolific Technology, Inc. PL2305 Parallel Port
Bus 004 Device 004: ID 050d:0119 Belkin Components F5U120-PC Dual PS/2 Ports / F5U118-UNV ADB Adapter
Bus 002 Device 002: ID 152d:2339 JMicron Technology Corp. / JMicron USA Technology Corp. JM20339 SATA Bridge

$ sudo /usr/lib/cups/backend/usb
DEBUG: list_devices
DEBUG: libusb_get_device_list=13
DEBUG: Printer found with device ID: MFG:Samsung;CMD:GDI;MDL:ML-4500;CLS:PRINTER;MODE:GDI;STATUS:IDLE; Device URI: usb://Samsung/ML-4500
direct usb://Samsung/ML-4500 "Samsung ML-4500" "Samsung ML-4500" "MFG:Samsung;CMD:GDI;MDL:ML-4500;CLS:PRINTER;MODE:GDI;STATUS:IDLE;" ""

[power cycle]

$ lsusb
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 006 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 007 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 008 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 009 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 004 Device 002: ID 04f2:0402 Chicony Electronics Co., Ltd Genius LuxeMate i200 Keyboard
Bus 004 Device 014: ID 067b:2305 Prolific Technology, Inc. PL2305 Parallel Port
Bus 004 Device 004: ID 050d:0119 Belkin Components F5U120-PC Dual PS/2 Ports / F5U118-UNV ADB Adapter
Bus 002 Device 002: ID 152d:2339 JMicron Technology Corp. / JMicron USA Technology Corp. JM20339 SATA Bridge

$ sudo /usr/lib/cups/backend/usb
DEBUG: list_devices
DEBUG: libusb_get_device_list=13
DEBUG: Printer found with device ID: MFG:Samsung;CMD:GDI;MDL:ML-4500;CLS:PRINTER;MODE:GDI;STATUS:IDLE; Device URI: usb://Samsung/ML-4500
direct usb://Samsung/ML-4500 "Samsung ML-4500" "Samsung ML-4500" "MFG:Samsung;CMD:GDI;MDL:ML-4500;CLS:PRINTER;MODE:GDI;STATUS:IDLE;" ""

[print job 11 - no printout]

$ lsusb
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 006 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 007 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 008 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 009 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 004 Device 002: ID 04f2:0402 Chicony Electronics Co., Ltd Genius LuxeMate i200 Keyboard
Bus 004 Device 014: ID 067b:2305 Prolific Technology, Inc. PL2305 Parallel Port
Bus 004 Device 004: ID 050d:0119 Belkin Components F5U120-PC Dual PS/2 Ports / F5U118-UNV ADB Adapter
Bus 002 Device 002: ID 152d:2339 JMicron Technology Corp. / JMicron USA Technology Corp. JM20339 SATA Bridge

$ sudo /usr/lib/cups/backend/usb
DEBUG: list_devices
DEBUG: libusb_get_device_list=13
DEBUG: Printer found with device ID:  Device URI: usb://Unknown/Printer
direct usb://Unknown/Printer "Unknown" "Unknown" "" ""
DEBUG: Failed to set configuration 1 for 067b:2305

------

for some reason the error_logs I've been judiciously saving are almost empty bar two lines with the following duplicated content in all:

W [15/Jun/2012:07:56:00 +0100] failed to CreateProfile: org.freedesktop.ColorManager.AlreadyExists:profile id 'ML-4500-Gray..' already exists
W [15/Jun/2012:07:56:00 +0100] failed to CreateDevice: org.freedesktop.ColorManager.AlreadyExists:device id 'cups-ML-4500' already exists

Saves trying to work out why I can't attach files to this bug report at least :-p