Sounds like it could be three things:
1) Their USD standard is bunk. If you're on a commodity money - or secondary exchange money - standard then you can only issue as many certs as there are units of that money in your reserves. With the XAU standard, you can't just mint gold certs without gold underlying it. That's not how any of this works!
2) They just FDR'ed their users, and took them off the USD standard but didn't tell them.
3) Less technically: sounds like they're skimming off the USD for themselves and hoping everyone doesn't divest at the same time. This could be either fraud, or it could just be incomitance, ignorance or any other *ance really.