Comment 4 for bug 1597719

I have the same problem here.
I initially installed Mint 18 Xcfe, then installed the KDE plasma (v5.5.5).

my xscreensaver seem to mess with some things, and this occurs even before I installed KDE, since I have also the problem that the screensaver starts (without really blocking anything, just the image appear) when listening from flash (youtube, soundcloud). I am not just listening, but actually doing something (mouse and keyboard).

It is very annoying, and turning off all some options (lock screen after X minutes) did not help so much.