Just minutes ago I was selling a shivering armor to my friend via secure trade. It took me 3 clicks to finally tick the box. I was clicking so fast that I accidentally clicked cancel immediately afterwards. I tried to tick the box again and once i did, it says my friend left the trade window, and he said thx, saying the transfer was successful. I went to my inventory and saw that the leather was still there, I swear that I only had one before trading... but my friend said he got one in his inv too. The gold also successfully transferred to me as well. This is a highly improbable bug that I'm pointing out.