Maguro does not swap between active and held call

Maguro is not able to swap between an active call and a held call. To reproduce the error:

# cd /usr/share/ofono/scripts
# ./dial-number A
# ./dial-number B

In this moment, A must be held and B active

# ./swap-calls

A should be now active and B held. However, this does not happen: B is still active and there is no communication with B. swap_calls returns with error "org.ofono.Error.Failed: Operation failed", due to RIL returning a GENERIC_ERROR when the operation is performed.

This looks like an error in the FW, because when we do a "list-calls" after dialling the two numbers, the output is

[ /ril_0 ]
    [ /ril_0/voicecall01 ]
        Name =
        LineIdentification = 681131111
        Multiparty = 0
        Emergency = 0
        RemoteHeld = 0
        State = active
        StartTime = 2013-12-03T08:50:43+0000
        RemoteMultiparty = 0
    [ /ril_0/voicecall02 ]
        Name =
        LineIdentification = 911521111
        Multiparty = 0
        Emergency = 0
        RemoteHeld = 0
        State = active
        StartTime = 2013-12-03T08:51:42+0000
        RemoteMultiparty = 0

Both calls are in active state, while the network actually has put the first call on hold (no communication with A at that moment). RIL is reporting a wring state.

NOTE: The functionality to swap between calls is only available in https://github.com/rilmodem/ofono at the moment, not in the Ubuntu package.