LibreOffice Calc Selected Cell Boundary is Invisible

Hi,

I've recently upgraded to Trisquel 8 with KDE Plasma 5.5.5. Overall, I'm very impressed. Especially having petsc-complex and slepc-complex available in the repositories as they are a pain to build from source.

Anyway, I have a really weird problem. In LibreOffice Calc, I cannot see the black box around the currently selected cell so it's hard to tell which cell is selected (I can work it out by looking at the highlighted row / column headers but it's not easy).

Any one know how to fix it please? More details available in my SO question: https://stackoverflow.com/questions/52615914/libreoffice-calc-selected-cell-boundary-is-invisible

Many thanks,
Steve