LuaLaTeX, Fontspec: Wordspacing and Letterspacing

Question

I have a command \work which will format titles in SmallCaps and with less letter spacing. Now the funny thing: If I try to add some word spacing, too, and only for SmallCaps, it affects the whole document, as you can see in the MWE. Any ideas how to achieve that the word spacing only affects SmallCaps or my command?

\documentclass{article}

\usepackage{blindtext}
\usepackage{fontspec}
\setmainfont[SmallCapsFont={Latin Modern Roman Caps},
             SmallCapsFeatures={LetterSpace=-6,WordSpace={3}}]{Latin Modern Roman}

\newcommand{\work}[1]{\textsc{{#1}}}

\begin{document}

    Immanuel Kants \work{Kritik der praktischen Vernunft}, \work{Kritik der reinen Vernunft} und \work{Kritik der Urteilskraft}...

    \blindtext

\end{document}

Answer 1

An acceptable workaround, which still let's you use \textsc without changing it, it defines a similar command \work which does have the desired spacing.

I think that there's absolutely no reason to desire this spacing: letters overlap! They need room to breathe…

\documentclass{scrartcl}

\usepackage{blindtext}
\usepackage{fontspec}
\setmainfont{Latin Modern Roman}
\newfontface\workcaps{Latin Modern Roman Caps}[LetterSpace=-6,WordSpace=3]
\DeclareTextFontCommand\work{\workcaps}

\begin{document}

Immanuel Kants \work{Kritik der praktischen Vernunft}, \work{Kritik der
reinen Vernunft} und \work{Kritik der Urteilskraft}...

\blindtext

\end{document}

Answer 2

After fiddling around with the same issue, I found the source of the «bug». It was the «Wordspace» feature. I am not quite sure that the «Letterspace» definition takes care of the spaces as well.

\documentclass{article}
\usepackage{blindtext}
\usepackage{fontspec}
\setmainfont[SmallCapsFont={Latin Modern Roman Caps},
             SmallCapsFeatures={LetterSpace=-6}]{Latin Modern Roman}
\newcommand{\work}[1]{\textsc{{#1}}}

\begin{document}
    Immanuel Kants \work{Kritik der praktischen Vernunft}, \work{Kritik der reinen Vernunft} und \work{Kritik der Urteilskraft}...
    \blindtext
\end{document}