Afaik Kingdoms/Retrofit does not fit 2H bugs but rather lowers the defense ratings of most units, thus making each of their attacks a kill.

The 2H bug affecting halberds, 2H hammers and 2H axes, and to a very small extent 2H swords basically is that those units attack very slowly and their attack animation gets interrupted due to auto-blocking animations against faster attack weapons. In addition to that, 2 of their 4 attack animations are harmless against infantry, and those 2 are the fast ones, thus leaving only their slow animation types as effective.

In a patched game, this problem still persists, but their animations are always effective against cavalry, so they are good cavalry killers but remain quite useless against any infantry.