I have discussed this "mientras que" with some people around and we agreed with Alec that the "que" in that kind of sentence doesn't sound natural, despite the fact that some of them accepted it as a colloquial construction. However, none of the examples we came with (except some similar ones to those of Pablo introducing a condition) were made with a verb in indicative.
And we also remembered that "mientras que" is a synonym of "en cambio", but it is also followed by a verb in indicative.
· Yo tengo mucho dinero mientras que tú no tienes nada.
I have a lot of money while you have nothing.
· Estamos todos celebrando mientras que Pedro se quedó triste en casa.
We are all celebrating, while Pedro has stayed sad at home.
· Voy a cocinar, mientras que tú no vas a hacer nada.
I will cook, while (I know that) you won't do anything. (Just to bring the original construction back... no subjunctive though.)