Black square behind toolbar icons

Hello, I am using libreoffice 5.1.2 (problem present in older versions too) in openSUSE Leap and Tumbleweed with the KDE plasma 5 environment

I notice a black (or blue) square behind many icons of the toolbar which is distracting when I work

There is a workaround to use UXA hardware accelaration instead of SNA but I cannot use this because it makes web browsing reaally slow.

What can I do to fix this issue?

Preview of the problem:

My laptop: Dell Inspiron 5558, i5, Intel graphics card, Nvidia 920m graphics card, 4 GB RAM

I just installed LibreOffice and am encountering this issue, using Calc. (I haven’t yet tried the other apps.)
Using macOS Sierra on a MBP Early 2011 model.

I’m surprised this hasn’t yet been answered.