Old behavior (Renoise 3.0):
Having defined an instrument with an effect chain routed to “track”, it would play back that instrument and feed it to the currently selected track. When the user would select a different track, the effect chain destination “track” was updated immediately. Live playing of that instrument would directly feed to the currently selected track.
The effect chain routing destination is now named “Current track”. The value of “Current track” (the track it is pointing to) is only updated after a “programmed” note (a note part of a pattern, as opposed to a note played live via a controller or keyboard) for the instrument has been played on a track. The track that “Current track” points to then becomes the track containing the last played note for that instrument.
For live playing I would strongly prefer the “Current track” value to be updated at the moment a different track is selected.