I have a 430 weapon with Deadly Navigation equipped in the Main Hand. My other two weapon choices are already-enchanted 420s, one with Deadly Navigation and one with Versatile Navigation. I have the 420 with Versatile Navigation equipped currently, so I don’t have to buy another enchant. BiB wants to equip the other 420 and re-enchant it. This is probably technically correct since that weapon has better stats, but the final DPS difference reads as 0%, so I don’t believe that it should be suggested.
Obviously this is a non-issue and I will just ignore it, but it’s a corner case example that I hope is helpful in some way.