Comment 7 for bug 1714302

I'm afraid the problem is deeper, see below.

When you attach new display, the mirror option is grey (in minimal dialog and in standard dialog too, no patch #53 applied). Then you can enable deactivated display in standard dialog, but it don't enable mirror option in my case.

xfce_randr_clonable_mode checks for same mode on both displays (same dimensions and refresh rate). My system uses same dimensions but different refresh rates for two displays. Therefor in my case mirror option stayed disabled. But I can imagine it might gets enabled for others.

As consequence I made patch which check for correct dimensions only. When it finds it, it enables mirror buttons (minimal and standard dialog) and allows to select such mode.

Before I will post it there, I will check patch #53 from link too.