It isn't really possible to add a test for this, since the issue was that the specific fonts require hinting in order to be legible at all. FreeType keeps a list of signatures of these sorts of fonts and the resolution to the issue was to add the fonts to that list. There isn't any way to test for unfortunately designed fonts which might be created and used in the future. All this is to say that there wan't really any bug in the original issue, the font was being rendered exactly how it should be and the fonts themselves are to blame. However, we try to make these essentially broken existing fonts render as well as we can for users who were unfortunate enough to need to use them but still discourage further production of such fonts.

In theory we could write a better detection algorithm than a blacklist in FreeType, but this would be an extra font analysis step for an extremely rare case. We also don't really want to encourage more of this sort of font to be created in the future, since there are much better ways to create composite glyphs in OpenType than relying on hinting instructions.