Pixhawk doesn't connect/boot under Ubuntu 14.04

I’ve had a similar behavior under 13.10, but I plugged in/plugged out and it usually worked again.

The port is visible as /dev/ttyACM0 as usual, but when I connect to it, there is no data.
When I connect my Pixhawk through USB I don’t get the usual beeping.

This problem is only under Ubuntu. When I run Windows - I have no problems. I connect it and after a few beeps and boops I have it up and running. I can also get it to work under Ubuntu when I connect before the system loads (for example during the GRUB menu).

Any ideas what might be causing this?

Works fine for me under 14.04, in fact much better than under windows which I usually have to replug it in random number of times before it works properly. And firmware updates are much, much more reliable for me with apmplanner2 on ubuntu rather than through mp on windows - they work every time, whereas mission planner is very hit and miss for me.