I don't think I quite understand what you are describing there. If a plugin is only assigned to one instrument but not the other, the other instrument's output should never be sent to the first instrument's plugin, not even during editing. Do you have a small example file to reproduce the issue?

Yes is hard to describe properly, maybe is my system only issue. In short -sometimes vst routed to #1 instruments can be heared on no routed instruments when I editing pattern.

Your system has absolutely no influence over plugin routing. The only thing I can imagine right now is that you use a plugin that does not clear its buffer when being stopped, which is often the case with reverbs. In this situation, you would be playing a note on instrument #1, then stop playback while the reverb on that note is still heard, and restart playback when entering a new note with a different instrument. In that case, the reverb tail of instrument #1 will still be heard with buggy plugins. Is this what you mean?

Yes something like that.

In that case, there is nothing we can do - we already ask the plugin to clear its buffer but if it doesn't do so, the old buffer contents will keep playing after restarting playback.