Boats (and other vehicles) sinking into blocks in zero gravity, players get stuck

[EzerArch]

• Minecraft version: 1.7.10
• Galacticraft version: From 488 and 489 on
• Forge version: 1614
• Single player (SSP) or Multiplayer (SMP)? SSP
• Galacticraft add-ons and other mods installed? No

Short description: Vehicles (e.g. boat) cause the player to glitch through the floor and fall to the Overworld. Depending on the condition, the player will either: 1) fall into the void with no damage. 2) re-enter the Overworld but get stuck at y=240.

The bug was introduced in the build 488 and the build 489.

How to reproduce

GLITCH 1: (from build 488 on)

1. Create a Space Station (anew or restart the client. World reload sometimes fixes the bug)
2. Place a boat on a flat solid surface, let it sink 1/2 of its height in the floor.

Note: if you place the bloat on the "ceiling", it will sink 1-2 blocks and may let you enter the space station.

3. GET IN THE CAR!... Uhu, I mean, get in the boat.

4. You and the boat will sink through the floor. This will cause a player desync. You will see yourself falling in the void with no damage, but internally you and the boat are not moving at all. If you fall to y=-64, the boat disappears, visually.
   

5. Press SHIFT (to dismount), you are teleported to the original point. The boat is still there, but invisible. Reload the world to get it back.

GLITCH 2: (from build 489 on, it's a sequel of #2247 😃)

1. Place a boat at the very edge. This avoids the glitch 1 and this:

2. Get in the boat and "drive" yourself into the Overworld.

3. Re-entry. You are stuck at y=240 bouncing on an invisible entity (the boat?) beneath the feet.

Expected behavior:

• the ridden entity will be spawned high in the sky above the Overworld (10 blocks below the player's sky spawn position, so if you look down you will see it)
  From: Player dies of suffocation in a wall if he falls from a SS riding non-rocket vehicle #2247 (comment)

4. Switch to creative mode with flight, and /tp <player> ~ ~-3 ~ and move up, the player's head will hit the invisible entity. You can't break it even in creative mode.

That's all.