... for more information.
It is possible that the driver just didn't load properly.
Brother make proprietary drivers for their printer/scanner combos too.
Of course, as this is to be an "always available" printer - perhaps you could disable the sleep function at the printer.
I have this feeling that it will continue to be fine; but if you remove it and then reinstall it, the wake function may vanish again. It is possible that the auto-functions in cups need to see a particular "thing" from the printer and the timing may be a little out so it gets missed.
(The likes of windows drivers will just assume a "sleep" printer is present and send a wake signal regardless - CUPS will be checking to see what driver options to set.)