Hi, I can confirm this problem. With Arm Exclusive selected, it will work properly
for a while (MIDI notes arming only one track at a time) then after a random period of time "forget" the setting, and will arm the newly selected track, but not disarm the previous track.
This is a worry as I am using Live 8.0.4 as a "sound module" or "MainStage"-type setup for playing keyboards with a live band. I have 16 of the programmable buttons on my Novation ReMote61 set to send MIDI notes which are mapped to 16 track arm switches. It's embarrassing when I suddenly play the sounds from two songs simultaneously.
I am not sending multiple MIDI notes at once as these are very deliberate button presses between songs.
Quitting and re-booting Live "fixes" the problem - until it faults again, after a random period of time.
Live 8.0.4
OSX 10.4.11
Novation ReMote61 (first model, not the SL) connected via USB