Comment 6 for bug 1714302

I think bug 11107 is somehow related to this issue that causes the mirror option to be greyed out. If you read through the comments in that bug report, xfsettingsd is not re-activating the display when it is turned on again. When the display dialog is shown, it does not know about the attached and/or reactivated monitor, thus it does not enable the mirror option. Interestingly, it does know that a second display is attached as it presents the options to extend or make the external monitor primary. Searching the code, it appears that the check for the clone option occurs in the xfce_randr_clonable_mode function (http://git.xfce.org/xfce/xfce4-settings/tree/dialogs/display-settings/xfce-randr.c line #651).The check for extended occurs in http://git.xfce.org/xfce/xfce4-settings/tree/dialogs/display-settings/main.c (line 2947).

I applied the patch from comment #53 and now on connect of an external monitor, the "mirror" option is no longer greyed out and is functional.

However, I'm noticing some unexpected behaviour as a result of this patch as well. After applying this patch and attaching an external monitor, my system automatically goes into clone (mirror) mode while the display dialog is displayed (even though my preference and previous state was extended). The dialog is functional and I can easily change it back to extended.