Okay, thank you very much for posting the log and the explanation. Your English is great, it's just I didn't work on Unfinished Business, so I wanted to make sure I didn't misunderstand.
So, yes: I checked .tp2 file and found out that neither line @23 nor line @24 work in .tp2.
It means two things:
1) it's a bug, the authors wanted to change the blade, changed it but forgot to change the description;
2) it's not a bug: the authors wanted to change the blade but didn't change it and the lines are just leftover lines from an earlier attempt(which is all right, not your fault - not a bug either, just an idea that never came to fruition).
I see that judging by the .tp2, sw1h27 remains unchanged, so I think it's 2): not a bug. If you had an Italian edition of Baldur's Gate 2, the item's description would be in Italian(with +2 THAC0, too).
(It's also possible that another mod added this blade, by the way. Not that it's true in your case, but it's just another explanation).
Bottom line: not a bug, not a problem, just two @tra lines UB no longer uses.