Question: How to use physics- Commutator/AntiCommutator and setup algebra rules?

For examples, they are two non-commutative variables x and y, and i use "Setup(noncommutativeprefix={x,y})" to define.
 As the previous results have shown that AntiCommutator(x,x)=0 and AntiCommutator(y,y)=0, so i just define Setup(algebrarules={%AntiCommutator(x,x)=0, %AntiCommutator(y,y)=0}).
When i am calculating AntiCommutator(x,y), the maple automatically simplifies the results and returns AntiCommutator(x,y)=0, as variables x and y are thought to be GrassmannParity =1 variables.

Consider two  3*3 matrix e23 and e32, the AntiCommutator of (e23, e23)=(e32,e32)=0, but the AntiCommutator(e23,e32)= e22+e33.

So how the algebrarules work and why there is the contradiction ?

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