thing is, the piano-roll is a MIDI clip editor, not a track editor, do you understand the difference?
on the other hand, you don't really need to close one first to open another. you can keep open all the editors at any given time--this of course might not be always optimal, depending on the window manger in charge, but may be a nice workaround; note that, among some other things, each clip editor position and size are saved into the session file so that it's restored on a later date and/or time.
also, the so called ghost track may give you a help in visualizing what's in that any other track, beneath the current editing clip;
thing is, the piano-roll is a MIDI clip editor, not a track editor, do you understand the difference?
on the other hand, you don't really need to close one first to open another. you can keep open all the editors at any given time--this of course might not be always optimal, depending on the window manger in charge, but may be a nice workaround; note that, among some other things, each clip editor position and size are saved into the session file so that it's restored on a later date and/or time.
also, the so called ghost track may give you a help in visualizing what's in that any other track, beneath the current editing clip;
you probably know all this already :)
cheers