I found and eliminated the problem this weekend. I had my rear shocks set way too short, and there was almost no downward travel in the suspension. I added about an inch to the overall length of the rear shocks and all is well.
By the way - These BC coilovers really ride like a dream. I'm about 10 levels down from full hard in the back, and 15 levels down from full hard up front.
Fresh Powder 2015 Versa S 5-speed - Work Euroline DH, BC Racing Extreme Low Coils, Tanabe front under brace, ARC Shift Knob, OEM-Style Fog Lights, Sound Deadening, Black Lower Grille Uprights, Mini Cooper Floor Mats, Chrome Door Handles. We need rear sway bars!