thanks for your reply, DarkStar. New points are automatically created in the lane that is not armed even if no controller is connected, just by starting playback.
In the following animation, I simply hit play and points are added in the lane not armed at the position where I started playback. In addition, the points are not just added ON the curve so that they would not affect its shape.
And yes, it is possible to draw the envelope no matter which automation mode is set but I don't consider this as a bug.
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