I have connected different devices (Moog Little Phatty, iPad synths, Yamaha QY-100, Macbook Pro) and all have problems with hanging notes on different MIDI channels.
I use a Combi with multiple split zones. Every zone has it´s own MIDI channel. The external devices are connected via standard 5-pin MIDI cable. (Only Kronos OUT to external device IN.)
I always(!) get hanging notes on my external devices via MIDI OUT. Only connections over USB work properly.
If I mute all timbres in my Combi I still get sporadic note off events!
The keyboard always sends on the global channel.
The consequence is:
I cannot use my Ipad because of
A) hanging notes over MIDI or
B) audio clipping over USB with most synth APPs. (On iPad 1. Maybe no problems with iPad>1?)

I cannot use my Little Phatty with my Kronos because of
A) hanging Notes over MIDI or
B) USB not possible because of wrong port. (Kronos and Phatty want to be slave to a Computer but not each other)
It´s a bloody mess.

Does no other use external equipment via old MIDI cables?
What do you experience with USB and MIDI connections?