Why is the order of amino acids in the output diagram of "gmx mdmat" messed up?

GROMACS version: 2020.3
GROMACS modification: No


I did the “gmx mdmat” command as follows:

gmx mdmat -f md_0_1.xtc -s md_0_1.tpr- meaning mdmat.xpm -frames mdmat2.xpm -no mdmat.xvg

But in the output diagram, which I attached, the order of the amino acids on the x and y axes is disturbed. What is the problem? And how can I fix the error?!

maybe gmx xpm2ps can help you to visualize better your matrix.