Endless momentum/ downhill force

Plattform PC, keyboard + mouse, Win 10 64bit

I came along to a bug I wasn't able to reconstruct on purpose, it happened two times with different vehicle and trailer:

I was driving the K700 + short logs trailer on proving ground and at a very muddy area, I stopped- but the vehicle didn't.
There was a slope so it was expected that the vehicle would move on a little bit, forced by the momentum, but even with deep mud and at the end of the slope it was not stopping, it was moving on. I put in neutral gear but it did not stop, handbrakes didn't work either, the vehicle and the trailer moved on. The brakes did work and stopped the vehicle but when released, it starts moving again O.o'
After crossing the whole muddy area on proving ground, there was a upwards slope, the K700 drove an it, stopped and started moving backwards...

The second time it happened with a C432011 + medium logs cart on the map level_river, same situation, the ground was very muddy and the vehicle (unloaded) started to drive uncontrollable.

To me it seems to be a problem with the downhill force and the momentum as there must have been a force that pulled/ pushed the vehicle nonstop.
Changing the vehicle didn't help. After I closed and resumed the map, the bug was gone. The bug seems to be very rare.

if you have a controller plugged in (on PC), it will do this sometimes. the controller could have a slightly stuck button. try smacking the triggers and see if it stops. also, turn the game off, unplug then plugin the controller, and restart the game. controller could also need calibration. you can also unplug the controller in the middle of this and use the keyboard thus deactivating the controller fixing the issue.

I have a Steam Controller but it is turned off. And if it would be a problem with the controller, the problem would be there all the time.
But it only happens when a vehicle stands or drives through mud and if there is a slope. It does NOT matter if there is a trailer attatched or not, I was driving a Zil130 without trailer and it startet to move without any input.

After releasing my map RoadTrip I had some feedback from people who had the same problem, trucks start to move by theire own when standing in mud. I had to remove some mud from my map so people were able to load their trucks which was impossible due to some mud at the loading area.

It seems the bug is related to the parameter SubstanceFriction in the media.xml.

<Mud>
<Substance
FullPushDepth="1.2"
LinResistance="10.0"
PushResistance="36.0"
SubstanceFriction="2.2"
/>

I changed the value 2.2 to 0.5 and the bug was gone- vice versa, increasing the value leads to permanent and massive boost whenever a vehicle has contact with mud.

For now, my solution is to decrease LinResistance to 9 and PushResistance to 28 and SubstanceFriction to 0.5 in order to maintain the characteristic of the mud but reduce the magical self moving bug.

Developer feedback would be nice!

@dereggen Newer had this happen in ST or MR in custom or default maps. (controller on or off)
Guess it has to be something with one or more of your files..?

Like I said, you can "force" this bug by changing SubstanceFriction. I would agree with you but it's not just me, I know several people who had this bug. With default and custom trucks, on default and custom maps.
Obviously SubstanceFriction is part of a mechanic that effects some kind of force that pushes vehicles forwards- the bug is, sometimes it does not stop, vehicles are moving without engine and even without driver.

Looks like your connection to Focus Home Interactive - Official Forums was lost, please wait while we try to reconnect.