The width of the logout/restart/poweroff confirmation screen depends on the resolution of the monitor from which it was selected. However, the notification is always being displayed on the primary screen.

If you have 2 displays with different resolutions eg: 1600x900 and 1920x1080, and you select the 1920x1080 monitor as being your primary, the width of your confirmation displayed on your primary monitor will will depend on the resolution of the monitor from which the action was activated. Doing this from the smaller display, the confirmation screen will spawn only 900 pixels from the 1080 available on the primary display. See attached pictures.

Reproducible: Always

Steps to Reproduce:
1. Have two displays of different resolutions connected. (Ex: 1600x900 and 1920x1080)
2. Set the display with a bigger resolution as your primary output.
3. Try to logoff from an action menu. 
4. Do step 3 from a menu that is located on each monitor.

Actual Results:  
The confirmation screen is appearing on the primary output with the width of the monitor from which the action was selected.

Expected Results:  
1. The confirmation should appear on your primary output stretching the whole width, no matter the place from which the action was selected.
2. The confirmation should appear on the monitor from which the action was selected, keeping the width of that respective monitor
3. The confirmation should appear on all connected monitors, each having the size of their respective monitor.

See attachments displaying both scenarios.