did you replace the rears with the EXACT same brand and model of tire? Different brands may have very slightly different circumferences. Generally though, if possible, with the same size tire (of course), if one's worn down and one's got more meat on the treads (hence, slightly bigger), you'd want the worn down ones in front.
I had worn out rears and when I put new fronts on, the torque gauge went bonkers, and engaged according to speed!!
In general however, I'd view a more sensitive AWD to be a good thing, so long as the power transmission is intermittent, and occurring at the proper moments (wheelslip, and simple acceleration).