I have used the brightness control with the Slackware distro. I believe that I had a laptop with Intel chipset. Though mine did not show the bar you talk about, as it would with Fedora, I believe that it may just be a software issue, maybe minor. Though I currently use Fedora, I have had experience with using Slackware. Anyway...if it is NOT minor, I suggest reading the information, or using another driver, if it comes to that. IF the brightness control works, and you get a static white line, and the screen adjusts appropriately, and the static white line is the ONLY issue, it may be a software thing.
When you say 'the bars', I guess you mean the control graph...it tells you where the brightness is as it is adjusted. If that is all, it may just be the X software on the distro...everything works, it is just that one thing. If it is something else, though, then I am unsure of what to say. Sorry, hope this helps