Urgot's Ult canceled by fiddle fear after full channel.

Just played a game in which I was playing urgot, I ulted a fiddlesticks and at the end of my channel (he must've been spamming fear on me or something) I was feared and my ult was canceled. Had it been in the middle of the channel or before the channel I wouldn't think it was a bug, but since it happened after the full channel, I can only assume it is a bug.