KP3 Question

I guess this question should be in off-topic.
I connected my EMX output to the KP3 input and (accidentally) connected my ESX output to the KP3 output. As a result, both EMX and ESX played and could be heard through the headphone jack of the KP3, but only the EMX was affected by the KP3's effects.
Does anyone know why/how this happened? Why/how is the KP3 output doubled as an input?
This oddity may become useful to someone one day.
I connected my EMX output to the KP3 input and (accidentally) connected my ESX output to the KP3 output. As a result, both EMX and ESX played and could be heard through the headphone jack of the KP3, but only the EMX was affected by the KP3's effects.

Does anyone know why/how this happened? Why/how is the KP3 output doubled as an input?

This oddity may become useful to someone one day.