Twin items that aren't game-generated dupes...

[the Langolier]

When dupes are created in the dungeon, the same item code spawns for each item, thus making dupes. In the case of your items, it seems like the very same thing happened, but a different item level was choosen for one so the codes are off only by one or two values. I've got two soldier's bastards swords like that too. I used a scanner to check the numbers and sure enough, one was tagged 19, the other 1A (25 and 26).

Just one of those things...