events not recorded when syncing to MTC

Hi,
I am trying to sync midish with ardour, using ardour as master.
Relocation and playback work fine but events are not recorded.

this is my ~/.midishrc:

dnew 0 "14:0" ro                # midi through Ardour is attached here
dnew 1 "135:0" ro               # vkeybd
dnew 2 "132:0" wo               # zynaddsubfx

and this is my rmidish session:
send EOF character (control-D) to quit
[0000:00]> inew vk {1 0}
[0000:00]> onew zyn {2 0}
[0000:00]> tnew pippo
[0000:00]> r
.. press play on ardour, timer starts on midish, press some notes on vk
[0005:00]> s
[0000:00]> p
..press again play on ardour but midi events are not played back
[0006:00]>

If I disable syncing (dmtcrx nil) events are recorded and played back.
Am I doing something wrong?

Thank you,
Stefano