Scale top key handles symmetrically

I'm trying to scale the key-handles of the tops of the curves in the graph editor symmetrically, like seen in the video, but I can't. Those are aligned ones. Though the handles move away symetrically when I pull, the curve only deforms in one direction to the right. Pivot point is set to individual centers.

Instead, the key-handles at the bottom, which have been changed to vector type, scale and deform the curve on both sides identically.

Thank you for your support!