Player stuck in block when changing from spectator to creative mode

The bug

Player gets stuck in block below when changing from spectator to creative mode.

How to reproduce

1. Enter a world in creative mode and don't move
2. Type /gamemode spectator and don't move
3. Type /gamemode creative and see how the player is stuck in the block below

The reason

This happens because when a player becomes a spectator they get lowered a little, so when they change back to creative mode, they are stuck in a block.