[luatex] Combining accents break monospace spacing with LuaTeX

[Trevor Spiteri]

With LuaTeX, using combining accents for Source Code Pro (otf) and
DejaVu Sans Mono (ttf) breaks the letter spacing. Latin Modern Mono
(otf) and FreeMono  (ttf) seem to work fine.

I get this issue with LuaTeX, Version 1.07.0 (TeX Live 2018). The issue
is not there in other software packages, and in particular the LaTeX
below produces an issue with LuaTeX but works fine with XeTeX, so I
think it might be an issue in LuaTeX rather than the fonts, though I'm
not sure.

\documentclass[12pt]{article}
\usepackage{fontspec}
\begin{document}
\setmainfont{lmmono12-regular.otf}
Combining: aȧa cċc. Not combining: cċc.
\setmainfont{FreeMono.ttf}
Combining: aȧa cċc. Not combining: cċc.
\setmainfont{SourceCodePro-Regular.otf}
Combining: aȧa cċc. Not combining: cċc.
\setmainfont{DejaVuSansMono.ttf}
Combining: aȧa cċc. Not combining: cċc.
\end{document}

Regards.

Trevor Spiteri