The Abel font @sgmentzer used in #253 is a good one to catch this kind of error because the difference between advance width and control point bounding box is so large and because the kerning is so extreme. It might make sense to make a test or two based on it -- but then we have some technical issues to solve about how to get it. (It's under SIL Open Font License, so we can just incorporate it, but that might be overkill).

This is a continuation of #4031 , but split off so that the other PR did not accumulate conflicts.