🚀 go-pugleaf

Some fonts I am working on contain a number of digraphs with diacriticals applying to the digraph as a whole. For example, one glyph consists of a "k" followed immediately by an "h", with an underscore running under both letters. As far as I can see, the best way to represent this in Unicode is "k" + Zero Width Joiner (uni200D) + "h" + combining macron below (uni0331). (The choice of uni0331 rather than, say, combining low line (uni0332) is not in my hands.) But when I place things like this in my liga file, nothing happens:

sub k uni200D h uni0331 by k_uni200D_h_uni0331

I have tried various approaches to work round this, but without success. It almost seems as if ligatures containing Zero Width Joiner have been disabled. Can anyone help/enlighten me? I am running the latest makeOTF on a MacBook Pro.

By the way, I am currently in India, and it will be difficult to consult this forum frequently. It would be a great kindness if any replies could be copied to my email address: jds10 AT cam DOT ac DOT uk.

John Smith