Recently someone reported that Iosevka's line height is inconsitent among weights, however the metrics in `hhea` and `OS/2` table are exactly same within all the subfamilies I provided.

It it means that there are still some undiscovered parameters which decides the line height?
TTF files :
http://7xpe0v.com1.z0.glb.clouddn.com/iosevka-lineheight-test-osx-20151224b.7z
Comments
I have seen this before and TBH I have no clue what is causing the different display in Font Book. It looks like a cosmetic issue to me and one can at least circumvent it by adding NameID 19 to the naming table.
Although actually the same effect shows up in the example above, it is less obvious than in the standard font overview.
Some layout apps use the top of the bounding box to position type.
Often, characters like Aring will be taller in the Bold.
After changing the hhea.descent to the "real" descender (-205) the problem is solved. But... Why OS X increases line height?
Can't for the life of me figure out why weights have different line heights?!