Tiamat bug?

While playing a game on Pantheon (doubble bruiser bot) i come across a problem with Tiamat where it was abit grey (just like when you buy an item you can't use) and i couldn't use it. while i tried selling and rebuying and other tricks in the shop it didn't revert to normal and the problem was left untill the end of the game.

I don't know why it apeared but when i made a new game it worked fine again.

If items help to identify the problem:

• Targon's Brace
• Bloodthirster
• Tiamat Bought in that order.

P.S sorry for the English, not a native speaker.