Why "Open Transactions cannot lie on your receipt"? FellowTraveller claimed here that :


  OT cannot lie on your receipt. It cannot change your balance or forge
  any of your transactions. (Bitcoin also is like this, but it's still
  worth mentioning.) Combined with an auditing protocol, this makes it
  possible to run low-trust servers.


Can anyone elaborate on this? What prevents the operator of an OT server from changing balances and forging transactions?
It is not possible for the OT server to forge your signature because you retain the private key. Sure, it could issue fakes but anyone actually checking the signature would immediately see that it is incorrect and reject the transaction.