Student loan debts and tax returns?

Okay, so i've got some student loans that are in default, and i am doing the rehabilitation program for them right now, and i get a letter today from the treasury saying that my federal return was funneled to the collection agency to help pay off the loan - i thought that wince i am rehabilitating them right now, that they couldn't do that - does anyone know what the criteria for decisions like this are? and do they do this with all student loan debts, or only ones in bad standing?