Try flashing a CM7 based ROM, then look under the general settings in the CM settings. There are a TON of light settings. If you turn everything off your buttons should light up. If you turn on some of the automation, you may have to dig into the menus and set brightness levels, etc.
I can charge all the time (work from home FTW), so I leave my brightness set on solar flare mode, so my lights are always on. I know that on CM7 if you turn on some of the automation, the default has some thresholds set for the backlights. You may want to search around on XDA, too, I think there is a thread on how to set all that up.
Not saying that you should go to AOSP to fix the lights, BTW, just a troubleshooting step to make sure it is not the ROM or a setting.