Hi,

Since Plasma 5.8, a fullscreen app like MPV disables compositing. That's due to this [1]. So, i was watching a video for some time and noticed the clock on my other screen (dual screen setup) to stay the same all the time. It turns out that the clock in non-compositing mode stays at the time when you last started plasma.

The clock i'm talking about is just the default plasma clock in the default panel.

You can reproduce this by:
1. Start plasma
2. Wait a minute or so, just till the time changes.
3. Open an app that disabled compositing.
4. - while compositing is disabled! - look at the time.

[1] https://cgit.kde.org/kwin.git/commit/?id=996ee34e14ece93421fee7bf7447ecfa785871d1