Created attachment 117819 [details]
Screenshot

SUMMARY

See the attached screenshot - there are two 1-pixel bright blue vertical lines on the right, near the scroll back + 1 horizontal line at the bottom, between the Konsole's window and the panel. These 1-pixel lines are actually desktop's background image showing through the Konsole window. One of the vertical lines (left one) is sometimes repainted black - but a scroll-up in history brings it back. I am not sure if it is konsole's bug or window manager's - please reclassify if necessary.

I don't see this issue on a 1920x1080 screen, only on 3840x2160 - which makes me think there is a rounding error somewhere...

STEPS TO REPRODUCE
1. Install Kubuntu on a system with 4K screen
2. Run Konsole and maximize the window
3. Observe 

OBSERVED RESULT

1-pixel wide lines of background image inside Konsole's window.


EXPECTED RESULT

Konsole's window covering the whole window's area.
SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Kubuntu 18.10, Konsole 18.04.3, 
(available in About System)
KDE Plasma Version: 5.13.5
KDE Frameworks Version: 5.50.0
Qt Version: 5.11.1