Shift Selecting Systems doesn't let you merge systems

[ATranimal]

For some reason, merge systems button only works if you drag select, not if you shift select two systems.

[ATranimal]

On further research, it appears that for some reason, shift selecting doesn't trigger any observable actions, namely that it should trigger both the 'object:selected' and 'selection:created', and actually does neither. There doesn't seem to be any action triggered when using shift select, but it does get triggered only on drag select.