Anyone come across a bug where, upon attempting to perform an enchant in the trade window, both people disconnect simultaneously, the enchant doesn't happen, and all the materials are lost, along with whatever was being traded?

Ouch... hope a GM helps you out on this.

And no, I haven't heard about this happening in my guild... at least not yet.

Nope. Have you been able to reproduce it?

Was he trading you items at the same time as you enchanted his gear?

I had a similar problem a while ago (no items lost, thankfully). I tracked that problem down to the extra items. Specifically, I had the mats on me, so I did the enchant at the same time that he gave me the mats. However, my bags were full, and somewhere between having the enchant go through but the trade fail, we'd get disconnected. The problem went away once I freed up some bag space.