Hello, sorry for the English speaking in this thread.
I have the same issue as greja: I’m in linux Mint 18.3 (based on Ubuntu 16.04, the latest long term support).
As greja I’m able to send note in messages to Iannix with format:

00:03:56:861 : midi://midiin note 1 62 (D4) 63
00:03:57:062 : midi://midiin note 1 62 (D4) 0
00:03:57:262 : midi://midiin note 1 62 (D4) 67
00:03:57:412 : midi://midiin note 1 62 (D4) 0

but whatever attempt I do on Midi Ports and even if the messages seems fine no Midi output messages are seen (I use a Midi monitor utility). Please let me know how can I help the debug of this issue.

Best regards,

Alberto