Solo modes for the Key and Drum editors, should be separated, i.e., just because you leave one editor, it should not mean that the solo status is carried across, since why would you want to listen to drums or percussion on their own, unless of course, you specifically selected solo in the Drum Map editor.
This is a workflow issue and unless you regularly switch between editors, as I do, programming music, then it may not be much of a problem but for me it is quite hampering to my workflow because there is no reason for the situation to be as such, other than because it is the way it has been for so long.