I can't see any recent posts that point out this bug, and I'm not sure if any other merchants are affected by it. This is all I've noticed so far.
When browsing what items Haggie had for sale, I noticed a fully-charged Diamond-Edged Pickaxe in his supply and I tried to purchase it. Haggie also had about 30 non-charged pickaxes and 30 with one charge. When I checked my inventory after purchasing the fully charged one, I noticed I was given a pickaxe with one charge (Item #58817114). This isn't the first time I've noticed this bug, a few weeks ago I tried purchasing a used broadsword for it's normal price, but was instead given a value modded broadsword for whatever high price is was.