Firefox installer fails in raring

As part of Kubuntu Raring Alpha 1 testing I tried out the Firefox installer and it claimed to have installed the package, but it didn't. From auth.log, it looks like permissions are correct:

Dec 3 12:04:52 kitterma-Inspiron-1011 polkitd(authority=local): Operator of unix-session:/org/freedesktop/ConsoleKit/Session2 successfully authenticated as unix-user:kitterma to gain TEMPORARY authorization for action org.kubuntu.qaptworker2.commitchanges for system-bus-name::1.64 [/usr/bin/qapt-batch --install firefox] (owned by unix-user:kitterma)
Dec 3 12:05:42 kitterma-Inspiron-1011 polkitd(authority=local): Operator of unix-session:/org/freedesktop/ConsoleKit/Session2 successfully authenticated as unix-user:kitterma to gain TEMPORARY authorization for action org.kubuntu.qaptworker2.commitchanges for system-bus-name::1.68 [/usr/bin/qapt-batch --install firefox] (owned by unix-user:kitterma)

Note: I tried more than once.

The related entries from apt/history.log are empty:

Start-Date: 2012-12-03 12:04:55
End-Date: 2012-12-03 12:04:55

Start-Date: 2012-12-03 12:05:45
End-Date: 2012-12-03 12:05:45

So I suspect qapt-batch is implicated.