For some apps, windows do not quite maximise

[LinuxOnTheDesktop]

On Mint 19.1 Cinnamon (the alpha version and the release version), for some applications such as Ksystemlog, windows end up such that the larger of their two toggle states is almost, but not quite, full-screen. That is: pressing the maximise button switches between (1) a smaller version of the window and (2) an almost-but-not-quite full screen version of the window.

The behaviour quickly reoccurs after one has resized the window of 2 to actually be full screen, i.e. even after manual correction, maximise does not really maximise. I find that if I use one of Mint Cinnamon's inbuilt themes, e.g. Mint-Y-Dark, the problem does not occur.

I am unsure whether there is a pattern to the applications affected. Perhaps they are all and only Qt apps.