I use the Apple-Remote on Imac alu.

The Brightness-Control works fine, when I put it in The Root-level of a personal self-created menu, where no further left-press-level-up exists.

For me, this solution works fine, nevertheless the mentioned bug remains. 
The long-left-press of the button you mentioned should not be the problem, because in the same menu-level just above the brightness-control i have volume-control-slider, which works as it should.

The described menu i used is "Einfaches Profil" - "EyeTV" and into the "Kontextmenüs"-"EyeTV" I drag-and-dropped the "Bildschirmeinstellungen"-"Helligkeit von Imac" item.

Thanks for the quick answer before!

c u georg