Oh and for what it is worth, on my '96 Subaru "L" sedan with AWD, ABS, and 4EAT Automatic transmission, I was only really aware of the AWD kicking in when driving in snow or ice.
I found that punching the throttle at low-speeds while cornering on limited traction surfaces, definately gave me a rear-bias on acceleration. The back end came out in what could best be described as a traditional "power-slide".
EDIT: Another thought... Have you tried driving in an empty parking lot, making very tight turns ?
Even at slow speeds you should detect an "imbalance" between the front and rear axles.
I first noticed this condition when making an illegal "U-Turn" on a hard surface public roadway.