When trying to assign either my X-Session, MK-461c or controls from PureData via MIDI Yoke, I get the same problem - When in MIDI assign mode I click on a live parameter, move the MIDI control and nothing gets assigned until I press the button in Preferences, MIDI/Sync to switch the controlle Remote to Off.
Then it seemingly releases the MIDI message like it's been heldin a buffer or something and it's assigned to the parameter.
I checked with Live 4 and all MIDI assigning fine there