Rebooting the device is mandatory to make this tweak work.
Normal /var/log/syslog :
Jan 4 18:46:08 Xvolks kernel[0]: Sandbox: ignoring builtin profile for platform app: /private/var/stash/Applications/iBooks.app/iBooks
Jan 4 18:46:09 Xvolks iBooks[954]: MS:Notice: Installing: com.apple.iBooks [iBooks] (675.00)
Jan 4 18:46:09 Xvolks iBooks[954]: MS:Notice: Loading: /Library/MobileSubstrate/DynamicLibraries/Activator.dylib
Jan 4 18:46:17 Xvolks UIKitApplication:com.apple.iBooks[0x7a8d][954]: DictinaryServices: Dictionary cache was updated
