When you select A([2,3],[3,3]), you're selecting four points. It's easier to understand in this case:
A = [1,2,3,4;
5,6,7,8;
9,10,11,12;
13,14,15,16];
A([1 4],[1 4])
Note that you're selecting the intersection of the specified rows and columns. Since there are two each, there are four elements being selected.
The way around this ambiguity is to use linear indexing
A = [1,2,3,4;
5,6,7,8;
9,10,11,12;
13,14,15,16];
% convert to linear index
idx = sub2ind(size(A),[2,3],[3,3]);
% index into A
A(idx)
