[xrandr] Wrong render with 'DoubleScan' in --addmode

[Rm Beer]

Adding the option stops rendering the graphic desktop to see only a
gray screen. (you can also see a small black square in the upper left
corner)

I would like to find out more about the problem and know what really happens.

SO: Linux 5.11.16-arch1-1.0 #1 SMP PREEMPT Fri, 23 Apr 2021 09:28:54
+0000 i686 GNU/Linux
packages:
mesa 21.0.2-1.1
libdrm 2.4.105-1.0
xorg-server 1.20.11-1.1

This problem has existed for 5 years, and you have the same problem
regardless of the monitor, machine, or system you use.