[LAU] Trouble with Alsa MIDI connections

Hello, I have two machines running the latest UbuntuStudio. On one of them MIDI is working fine, but on the other I am having problems. On the problem machine I can't connect either of my external MIDI keyboards to another MIDI port while Jack is running. If I highlight the keyboard and the other port in the QJackCtl Alsa graph and click "connect", nothing happens. I can however connect them while Jack is inactive, and that connection will continue working even after Jack has started again. I am also having a problem with an application running in Wine (Reaper). Reaper's MIDI port does not appear in the QJackCtl Alsa graph, but Reaper shows the other MIDI ports available in Alsa in its own preferences. However if I try to connect it to either of my external keyboards it fails, and it does so regardless of whether Jack is running. It will however connect to MIDI Through (which gave me a reasonable workaround when my routing requirements were simpler than they are now). Does anyone know what I need to do to get MIDI connections working properly? Many thanks