When playing on a server, we were riding vehicles (boats & mine carts) after a certain distance the player in a vehicle became invisible to others, but remained visible client side.
*What I expected to happen was for to player to be visible.
*What actually happened was he turned invisible, but the vehicle still moved
Steps to Reproduce:
1. Get in a vehicle, boat or mine cart
2. Travel around 100 blocks
3. The player will not appear to be in the vehicle from other player's screen.
*the player becomes visible after the vehicle is destroyed.
Linked issues
Comments

It also happens to entities such as villagers.
Confirmed, exists in 1.4.2.
It's a pretty annoying glitch, I went by boat and while I spoke with my friend he said it looked like I was going in totaly different direction by foot ⚠️ .
Duplicate of MC-84?
Probably.
Note some times the player will also go invisable once the boat is broken, i play a PvP map a lot that uses boats, when i shoot the boat (with the invisable player in it) the player stays invisable shooting arrows at me and i have no clue where he is lol.
Still happens in 1.4.4. More specifically:
build a long track (>400) from A to B
first player takes a ride with a cart from A
after first player ends at B second player starts
second players arrives a B and is invisible even after leaving the cart
first player rides back from a B to A and finds second player hanging in midair along the track.
Still existing in 1.4.7, confirmed using the latest minecraft_server.jar and vanilla clients:
1. Player 1 gets into a vehicle near player 2(Tested with pig + saddle & minecart separately)
2. Player 1 rides vehicle out of player 2's render distance, vehicle despawns but player 1 remains in riding position in the air for a few moments.
3. Player 1's playerentity is then moved to where they boarded the vehicle and remains there in a stationary sitting position until player 1 dismounts the vehicle.
4. Any other players encountering player 1 int he vehicle will simply see the vehicle and not the player. Player 1 can still fire arrows and otherwise interact with the world from the vehicle that they are riding, to player 1 everything seem to be working as expected.
this bug still exists in 1.5.2!
me, the same case, in my case, the player stays there, where he/she entered the boat
I can confirm this issue!
Just a note, the player will appear at a location (sometimes where they entered the vehicle) and float until they exit the vehicle.