Values in timing_curves outside of [0,1]

[trethaller]

We are integrating Keyframes in our project using AE CC 2018. We noticed that timing_curves sometimes contain values greater than 1, which using our bezier interpolation is causing the interpolation to overshoot the range of previous-next keyframes values (control points end-up outside the [0,0] [1,1] window).

For example:

Exports to:

{
          "property": "X_POSITION",
          "key_values": [
            {
              "start_frame": 3,
              "data": [
                992
              ]
            },
            {
              "start_frame": 1559,
              "data": [
                861
              ]
            }
          ],
          "timing_curves": [
            [
              [
                1,
                2.61756432200488
              ],
              [
                0.76461011577208,
                1
              ]
            ]
          ]
        }

The 2.617564.. value seems to be caused by the very long yellow curve handle on the first point. Is that expected? If so, what interpolation formula are we expected to use to stay within the keyframes range?

-- Edit: Here is an example of what cubic bezier interpolation gives for control points (1, 2.6) and (0.76, 1) http://cubic-bezier.com/#1,2.6,.76,1