I don't know if this is just me (this happened before I killed Yaga-Shura), but I got a bug where after cespanar tells you that you can upgrade the ravager, he told me I could upgrade the firetooth (something I didn't have) with the bowstring of Gond (Something I couldn't have) for just 5000 gold. For fun, I said yes and Firetooth +5 was in my inventory.
The mods I have installed are, in this order: Baldurdash bugfixes, Kelseyv1.0.3, Ascensionv1.4.12, Expanded Theives guild (version unknown, though relatively new), Illyichv4, Tashiav2.05c, Item-upgradev17, Solaufienv71, Spell-50v3, Valenv26.
Can somebody guess as to why this happened?