I have noticed the same thing on a few of my maya renders, it seems to occur when you use translucency on materials along with standard maya area lights, i noticed that reducing the translucency attribute on materials fixed the problem but means i could'nt have nice physical lighting with translucent objects. this may be a rendering artifact from some other issue but i'd try turning off any translucency on shaders first and also try using spots instead of area lights and see if it fixes the problem!

Hope this may be of some use, alias were ment to be addressing this in maya 5.0 but i think the same things seems to happen, try rendering in mental ray and see if it does the same thing.

Regards,

Sam