The report
A player on 7daystodiemods wrote in: on a friend’s server, he backed under a van, the secure cycle finished, and the van stayed where it was. The truck slid out from under it, then got launched when the coupling broke away. His friend, the host, could couple the same van with no trouble.
On our own server
Taroos ran a dedicated server of our own for the first time and joined it as a player. It happened exactly as reported: coupling worked for the host and for nobody else.
The game hands a vehicle’s physics to whoever is driving it, and a parked van belongs to the server. The mod coupled the van on the driver’s own machine and never told the server, so the server kept holding the van in place while the truck pulled on it.
The fix
The driver’s game now runs the whole rig. When you couple, your game takes the van along with the truck, tells the server, and sends the van’s position about twenty times a second so the server and every other player see it follow. Release, get out of the truck, or leave the game, and the van goes back to the server. Single player and the host work exactly as before.
Taroos drove it as a joined player on our server: three rounds of couple, drive and release, with the van keeping pace with the truck up to about 60 mph and never breaking away. He got out while coupled, walked around the rig and got back in, and the van stayed coupled. We haven’t yet had a second player watch the rig from their own game; if you do, tell us how it looks.
Release from the driver’s seat
You release the van from the driver’s seat, by design: H, D-pad Down, or Release trailer in the seated hold-B menu, with the truck stopped. The 1.6.1 README still listed the truck’s menu from outside; the README now matches the mod.
V2.6
The V2.6 download carries the same fix. Taroos drove it on V2.6: coupled, towed, released from the seat and coupled again, with the van matching the truck the whole way. The multiplayer test itself ran on V3.2.