Some snowshoes will flip up more snow purely based on their design.  You most likely purchased a snowshoe with a "fixed binding" where heavy duty straps are used underneath the binding.  This type of binding has the advantage of giving you some shock absorption and side to side flex in uneven terrain.  Stepping over obstacles and backing up is also a bit easier because the tail of the snowshoe does not drop away as much from your foot.  The disadvantage, as you noted, is that the is a tendency for snow to be kicked up onto the backs of one's legs.  Atlas's SLS (Spring Loaded Suspension) is a common example of a fixed binding.

It is most likley the brand / style of snowshoe that you use, I would try the MRS.

Curious.  What brand and model snow shoes do you have?