Make a track with some notes that are sent to virtual midi track 4.
Make a track in another page that is set to midi ch 3.
Press rec so it blink orange. Press and hold a step in the track like you want to make "step note recording". Now the track will be fed notes from the virtual midi track.
This is not "leaking" per se, it is just the fact that step recording is defined to be input channel agnostic. It is therefore not bound to virtual channels, but you can verify it with an external keyboard – step recording will work on any channel.
We can of course discuss separately (in a feature topic) whether it would be preferable to have it otherwise.
Ok, I see the reason for the "leak". But too me it seems like something that should be worked on at some point, since it renders step note recording almost useless if you are using any virtual midi channels at the some time.
As I see it maybe step note recording should only "listen" to incoming midi and not to virtual midi.