EDIT: Original thread title was:
Opening/closing docked MIDI Editor can cause irretrievable loss of arrange zoom
Discovered it's not MIDI Editor specific after this thread started:
https://forum.cockos.com/showthread.php?t=200642
It happens when a docker area has it's first/only window opened or last/only window closed, or docked/undocked. In other words, when the docker itself is opened or closed. Scrolls to the "last touched track".
EDIT 2: tested with 5.78 on windows 7x64
Original report and gif made with older version roughly current with date of OP.
-- Original Post Below --
Has this been reported? It would be one for window management section.
Opening/closing docked(attached) MIDI Editor can cause irretrievable loss of arrange view vertical scroll
I say irretrievable because unless you have done something like horizontal scroll/zoom at the previous level, you cannot get it back with SWS Undo Zoom.
I think selected tracks or maybe last touched track might have a bearing on it so if you try to reproduce make sure the higher numbered track is not selected. Which means you probably can't have click in arrange changes track selection preference enabled.