Disabling Mirrored MIDI Editing
To disable Mirrored MIDI Editing, do one of the following:

Deselect
Options > Mirror MIDI Editing.

Deselect the Mirrored MIDI Editing button in the Toolbar.

If Mirrored MIDI Editing mode is disabled, and you edit notes of looped clips in Notes view, the edit flattens the loop. Similarly editing clip groups separates the clip groups.