Blender 2.54 + luxblend25 + luxrender .7: render problem

After some 9 hours of rendering, I’ve got a very weird problem. The scene is lit with a single “softbox” a light-emitting mesh above the objects in the scene, slightly in front of the mug in question (attached). I’ve got one more object that serves as emitter, but it emits very little light, so it has no effect on the mug.

Can anyone please tell me what is going on? The scene hasn’t cleared up yet (probably due to excessive usage of glossy material (?), but if the mug doesn’t get fixed any time soon, I guess I can edit it in image editor and fix that part…