Bats fly in the perched position and vertical movement is not smooth

Bats correctly enter the flying animation when they start flying after hanging from a block so this only affects bats that are spawned or reloaded while already flying, which seems to be the case for all naturally generated bats. Bats spawned using a spawn egg or /summon minecraft:bat ~ ~ ~ {BatFlags:1b} correctly enter the flying animation.

The glitch affects both rendering and calculations on the client, as with hitboxes enabled the bat's hitbox is positioned as though it were hanging.