Vertical metrics help for Yosemite font replacement

(not sure what section this best fit in, sorry!).

A couple of weeks ago I was happy to discover someone had made a System Font Patcher for Yosemite. It is a clever script that uses fontforge to change the names of any fonts to what the system expects Helvetica Neue to be. I am not the creator or the maintaner of the project, but I've happily used it to replace my system font to Source Sans.

However, it has a few bugs, among them a glitch in vertical metrics in some situations. The owner of the project is asking for help in sorting it out, and I thought I'd just pass it along here in case some savvier person can lend a hand for the greater good.