Shift after mora and old bar spacing algorithm don't play nice together

[rpspringuel]

When using the old spacing algorithm, the text under a bar does not shift to the left with the bar when the bar is preceeded by a punctum mora, resulting in a mis-alignment of the text with its bar.

\documentclass[12pt, a4paper]{article}

\usepackage{fontspec}
\usepackage{fullpage}
\pagestyle{empty}

\usepackage{libertine}
\usepackage[autocompile]{gregoriotex}

\begin{document}

\gresetbarspacing{old}

\gabcsnippet{(c3) first(g) *(:) sec(g)ond(g.) *(:) third(g) (::)}

\end{document}

The first asterisk aligns correctly, the second does not: