Maximised windows won't fill space after a reboot where the resolution is larger

This effects 32-bit Lubuntu 16.04.1 LTS, when a laptop is plugged into a 1920x1080 monitor through HDMI and the laptops display is off. Whilst logged-in my resolution is set to 1600x900 so that it scales correctly, when it is set to 1080p the edges of the screen are outside of the monitor, but it looks fine in 1600x900.

However when it reboots the booting up process and the login screen are in 1920x1080, (in-built laptop display is also on during log on) once you've logged in it changes back to 1600x900, however when you maximize a window it only takes up three quarters of the space until you cause it to redraw, this can be done by changing the resolution then changing it back, or by changing the size of the task-bar. After doing that all windows will now take up the full space.

I do have Docky installed, by turning that off doesn't help, I'm also not using any restricted graphic card drivers. But I do have Compton Composition manger installed and use a config file like this: http://duncanlock.net/blog/2013/06/07/how-to-switch-to-compton-for-beautiful-tear-free-compositing-in-xfce/#id8