As far as i can tell from the wiki there is no exceptional set bows...

I think it might have just been bugged and have been the Warder's Tempest but the Daimyo's Yugen is actually a bow as well, though the Wiki says it's a trinket. I'll fix that.

That's a really weird bug. I looked at the table and don't see how that happened. I'd like to know what the stats were going to be. lol

^just got the same issue. Just had "Umbral Sword discarded" message, green text so it should be a normal set item ( my filter for set items is on normal), but there's none with that name iirc.
Maybe just a color problem? Could be just a normal rare item...

Possibly... Hmmm..

I can't even find anything called an Umbral Sword. Umbral Hammer, perhaps?

Pretty sure it was Umbral Sword, but I'll have to check this evening, I'm at work right now.
I'll let you know, but it's nothing major anyway...

Edit : Umbral Sword confirmed.

When an item that is discarded is shown on the drop list, it shows you the base item name, regardless of the quality.

So all these strangely named set items and uniques are in fact just the base item.

(That's my theory anyway )

^but that doesn't really explain what item it is,at least in the OP ( no exceptional set bows exist ingame )...

Daimyo's Yugen, apparently is.

My guess as to why it was listed wrongly in the wiki originally is that the slot is probably simply named "trinket".

^ forgot that the Daimyo piece was changed to a bow... That explains it.

It's weird how I said that literally the first comment