I've run into another MIDI-related bug. This is a showstopper!
I am using the unreleased 7.1.17 version under MacOS Yosemite.
I've assigned MIDI controls to all four master faders.
Using the MIDI controller, adjust all the master faders several times to extreme values (-100% to +100%), back and forth.
Continue to use the MIDI device to adjust all the master faders for maybe 30 seconds. Switch between viewing panels Buttons #1 and Buttons #2 in Live.
Soon, Live will lock up and stop responding to any buttons or MIDI controls.
ShowXpress must be quit and restarted.
I can make this happen again and again, though the time required varies.
Support -- Can you reproduce this?