That's a phenomenon known as light leak. That happens with radiosity. I'm not sure if you can call it a bug, it's a secondary effect of the radiosity engine in Vue. It's not directly related with your lighting. It's not related with Poser characters either, it can happen with anything.

There are several things that influence this effect. From the top of my mind, here's some:
a) if your characters have some self luminosity, even if small, this effect increases. SkinVue applies a certain luminosity to skin, for example, to fake SSS.
b) if you have very thin objects, like planes, that also increases the effect.
c) if you have radiosity gain, it also increases

I'm sure there are more, but I can't remember now.

Some ways to decrease it, other than counter-acting the effects above, again from top of mind, not an exaustive list:

1. increase your advanced effects setting in the render settings
2. if 100% is not enough, edit these effects and apply custom radiosity photon map. Decrease the maximum gathering radius, increase number of photons, etc.

Hope that helps.