A bug report has been around for about a year (#2579) but afaik the issue itself has existed for much longer: because the original engine used simple per-vertex lighting, Bethesda was essentially free to place as many light sources in a scene as they needed. More than OpenMW's per-pixel lighting renderer can handle. This results in buggy-looking areas where lights will blink on or off depending on the player's proximity to them.
There is excitingly little left in the way of a 1.0 release, but this will have to be fixed before then, and it seems like a doozy.
The issue has been discussed before, and Hrnchamd seemed to end it on a hopeful note, but that was 2012 and things might have changed. If anyone elucidate further on this - does OpenMW already have a game plan, or is a solution still far from certain?