Comment 2 for bug 2017670

I also had the problem that the buttons in the upper right corner did not always work when the window was maximized.

This affected Synaptic and gParted as well as Chrome.

The problem was caused by Anydesk displaying its icon in the systray. This caused the topbar area to be enlarged, but this was not visible.

After quitting anydesk and a relog the buttons work again.