[dev-context] small bug with the 'frac' font feature and linux libertine

Hi, One of Hans van der Meer’s notes has this definition: \definefontfeature[fraction][frac=yes] \definehighlight[textfraction][style={\feature[+][fraction]}] but 'frac' sadly does not quite work correct with Linux Libertine. It looks like somehow the substitution context is off when the command is used immediately after a digit? I am not sure how to debug this properly, nor how to fix it even if I could find root cause of the problem, so I am posting here in the hope someone knows how to fix it. (adding \hskip1sp works as well as a full space, btw) Example attached. Best wishes, Taco