MIDI is kinda like Microsoft standards - often ignored.
Yes if you look in a CC# Table it will say 86 is 'undefined' but that simply means the 'standard' has no definite pre-allocated parameter. You will see that many of the others are allocated to various things but that does not mean they are there only uses, they can be mapped to anything.
The standard just makes it easier for manufacturers to have some similarity. ie CC#7 is pretty much always Volume CC#2 Breath Controller etc, But not all of them are implemented or adhered to in all devices.
KMI use CC's to communicate with the SS app - CC# 40 -79 = 1-0 pedals, 80-83 = Nav, 86 = Ext. Pedal Not sure why they left 84 & 85 (Maybe they wanted #86 for Control ;-} )
Using a MIDIMonitor program allows you to view MIDI streams - thats how I figured it out . . .
So as to the why? SS uses this number , no particular reason . . .
KMI StringPort_1650, SoftStep_VK2 v1.2 & MIDI Expander; Mac_Moore Guitar,
Roland VG 8, 88 & 99, YamahaVL 70m; OSX 10.6.8, iMac i7 2.8G QC; MaxMSP 5.1.8, Ableton Live 8.2.2, M4L, SC3, QC, cSound, etc, etc,