OSX: no more sleep after 10.11 to 10.11.2 upgrade

Symptoms: Apple menu | Sleep causes the monitor to sleep but not the UC anymore
Diagnosis:

centurion:~ jerome$ pmset -g assertions
2016-01-07 08:07:40 +0100 
Assertion status system-wide:
   BackgroundTask                 0
   ApplePushServiceTask           0
   UserIsActive                   0
   PreventUserIdleDisplaySleep    0
   PreventSystemSleep             0
   ExternalMedia                  0
   PreventUserIdleSystemSleep     0
   NetworkClientActive            1
Listed by owning process:
   pid 245(cupsd): [0x0000048000110227] 00:01:13 NetworkClientActive named: "org.cups.cupsd" 
Kernel Assertions: 0x104=USB,MAGICWAKE
   id=500  level=255 0x4=USB mod=01/01/70 01:00 description=com.apple.usb.externaldevice.1d110000 owner=IOUSBHostDevice
   id=501  level=255 0x4=USB mod=01/01/70 01:00 description=com.apple.usb.externaldevice.1d113000 owner=Dell USB Keyboard Hub
   id=502  level=255 0x4=USB mod=01/01/70 01:00 description=com.apple.usb.externaldevice.1d114000 owner=Optical USB Mouse
   id=503  level=255 0x100=MAGICWAKE mod=01/01/70 01:00 description=en0 owner=en0
Idle sleep preventers: IODisplayWrangler

We can see that the culprit is cupsd, which is related to the printer driver.
Solution:
Uninstall the printer, then re-install it again and the problem is gone.