Now when moving keyframes in the Action Editor, any existing keyframes on the frames where a selected keyframe lands (after the transform) will be removed. This is to prevent stacks of keyframes which cause blips and headaches for animators (especially stressed animators with a looming deadline).
I've added an option to the Action Editor's View menu to turn this behaviour on/off (by default, it's on). This shouldn't need to be used too much, and may be removed in due course. If it stays, it'll need a better name...
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