MIDI input should use all selection types to determine note
There are two types of selections: you can select one element by clicking on it or multiple elements by clicking with the Ctrl key held down (no box appears) or you can select a range (a box appears).
When playing notes on my MIDI input device (*not* during note entry), the sound used is for the topmost instrument in the score if a range selection does not exist. If a range selection exists, the sound is the topmost instrument in the selection.
I would like to propose that single element and multiple element Ctrl key selections be treated the same way: the sound should come from the topmost instrument in the selection.
The problem is this: if I have a multi-instrument score, I may be working on, say, the piano part. I may play (on my MIDI keyboard) a passage I wrote. To get the piano sound, I make a range selection; otherwise, I will get the sound of the topmost instrument. I may try some variations on the passage and then make some corrections. Usually the corrections involve selecting notes, not ranges. If I try to play the new passage, I have to remember to again make a range selection in the piano part. I almost never remember, particularly if I am really concentrating on the changes. When I try to play the passage, I get the wrong sound and that reminds me to make the range selection. Meanwhile, I can see that I have a note still selected in the piano part.
Another way of saying this is: If you have a note selected in any fashion, the instrument associated with that note is most likely the one you want to assign to any MIDI input. Of course, if you have multiple notes selected, you have to apply the "topmost" rule, which is acceptable as most times only notes in a single staff are selected when I'm doing the kind of work where I need to play the MIDI keyboard.
There is no problem when entering notes. This particular problem only occurs when note input mode is OFF.