I am completely new to quantum computing and playing [QuantAttack](https://qniapp.github.io/quantattack/). While playing, I found something strange: SZS turns into Z.

According to [the Wikipedia article](https://en.wikipedia.org/wiki/Quantum_logic_gate) that the game recommends reading, SZS must disappear because:

$$
SZS = \begin{pmatrix}1 & 0 \\ 0 & i\end{pmatrix} \begin{pmatrix}1 & 0 \\ 0 & -1\end{pmatrix} \begin{pmatrix}1 & 0 \\ 0 & i\end{pmatrix} = \begin{pmatrix}1 & 0 \\ 0 & 1\end{pmatrix} = I
$$

Is there some weird quantum thing I missed, or is it just a game bug?