Nostalrius Begins - Quality wow vanilla realm (1.12)

I was selling Flask of the Titans for 60g a piece. A lvl 16 toon by the name of Zaco messaged me and We settled on 58g. He put the gold in the window and I put the Flask. WE both hit accept, at this point both item/gold were still in window. The screen lagged a brief second, and then went through (both gold/item still displaying). Once the trade went through, I had no gold from transaction, I was short the flask, and Zaco immediately logged off...

To be clear: 58g and the Flask of Titans were both visible AND highlighted in green. This isn't a case of him removing the gold quickly and both of us re-hitting OK.

Most likely an exploit on his end. Please help