When flying with elytra and using rockets, rockets will set player’s velocity to a set value. As a result, when the player is moving faster than that set value (which is possible since said value is apparently lower than minecraft’s terminal velocity), the player’s velocity will immediately change to that value or (in the case of changing direction) that previous momentum will be completely nullified and the player’s velocity will be set to the set value. This disobeys minecraft’s momentum mechanics

How to reproduce:

Wearing elytra, use /tp to teleport up to an extremely high y value and fly straight down until minecraft’s terminal velocity is reached. Then, when nearing the ground, use a rocket and immediately turn to fly parallel to the ground (or face straight up). The player’s (maximised) downward momentum will be immediately cancelled upon use of the rocket and the player will fly in the direction they are looking at ~30m/s for the duration that the rocket is active.