misleading "incorrect password" error when lacking permissions to unlock luks

When logged into a Ubuntu 12.04.2 server through x2go, I attempted to use the gnome-disk-utility (palimpsest from gnome-disk-utility 3.0.2-2ubuntu7) to unlock a luks encrypted filesystem on a removable device. I got the error "Incorrect Passphrase. Try again" even though I was using the correct passphrase (which I could use with "cryptsetup luksOpen" as root).

I believe the real reason I couldn't unlock the device with gnome-diskutility was that the default policykit org.freedesktop.udisks.policy only allows luks-unlock for "active" users. The policy is reasonable, but gnome-disk-utility should distinguish unlock failures because of insufficient permissions from "incorrect password".

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: gnome-disk-utility 3.0.2-2ubuntu7
ProcVersionSignature: Ubuntu 3.8.0-25.37~precise1-generic 3.8.13
Uname: Linux 3.8.0-25-generic x86_64
ApportVersion: 2.0.1-0ubuntu17.3
Architecture: amd64
Date: Mon Jul 1 23:02:56 2013
EcryptfsInUse: Yes
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
MarkForUpload: True
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-disk-utility
UpgradeStatus: No upgrade log present (probably fresh install)