http://www.ableton.com/forum/viewtopic.php?t=70835

Until now, when mapping MIDI CC to a on/off button, the button is
switched when the MIDI CC value crossed 64.
Now, it is possible to set up min and max value for such a mapped
button.
The idea is that when the CC value is between min and max, the button is
switched on (or off in reverse mode).
If the CC value is outside the min and max range, the button is switched
off (or on in reverse mode).