As a Geologist, I believe that flowing glass is not a myth. I'm not sure where people are getting their information that it was debunked. In geology, you can see solid materials that "flow" when you see rocks with curving layers. Since rocks and glass can flow, it would seem that all solids can flow to some extent. Even if glass isn't crystalline, many things that are solids are not crystalline, and and many things that are crystalline can flow.

Mythbusters also studied this and came up with the opposite conclusion.

While true that it is Jon Fishman's dress, it was made for him by Alyce Santoro (whose site you linked to).