Question: Confused with substitution

I have a matrix A and a matrix B defined as B:=A. When an entry of B is changed in my Maple code, the matrix A is also changed. 

A := Matrix([1, 1]):
B := A:
B[1, 1] := 2:

The result is

[2,1] but as you see, I did not change the entries of A during the code.  

This never happen for numbers. 

Please help me.

confused in matrix substitution

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