[Latency API] Jack midi always reporting zero latency

Hello, having trouble with the latency API.
I start Jack with this (the 6 periods are just for testing):

jackd -P30 -dalsa -r44100 -p512 -n6 -Xseq -D -Chw:M1010LT,0 -Phw:M1010LT,0

One Jack audio input port, one Jack audio output port,
  one Jack midi input port, and one Jack midi output port
  have been registered and connected to audio hardware ports
  and midi hardware port respectively. All is functioning.

The ports were created with these calls:
jack_port_register(_client, name1, JACK_DEFAULT_AUDIO_TYPE, 
JackPortIsInput, 0);

jack_port_register(_client, name2, JACK_DEFAULT_AUDIO_TYPE, 
JackPortIsOutput, 0);

jack_port_register(_client, name3, JACK_DEFAULT_MIDI_TYPE, 
JackPortIsInput, 0);

jack_port_register(_client, name4, JACK_DEFAULT_MIDI_TYPE, 
JackPortIsOutput, 0);


So far so good. But when I ask for the latency of the
  ports, the Jack midi ports are always reporting zero:

Jack audio client capture port:
Capture range: min 512 max 512
Playback range: min 0 max 3072

Jack audio client playback port:
Capture range: min 0 max 512
Playback range: min 3072 max 3072

Jack midi client capture port:
Capture range: min 0 max 0
Playback range: min 0 max 3072

Jack midi client playback port:
Capture range: min 0 max 512
Playback range: min 0 max 0

What could be wrong here?

Thanks.
Tim.