For a 4x4 input matrix, this method returns a 4x4 matrix as expected. Likewise, for a 3x3 input matrix, it returns a 3x3 matrix. But for input matrices that are 2x2 or 1x1, this method returns a 4x4 matrix (filling in only the upper left 2x2 or 1x1 entries).

This causes a problem when one needs to continue with matrix math operations on the result. For example, if P and R are both 2x2 matrices, the following will throw an exception:

MatrixF K = P.multiplied(P.added(R).inverted);