An easy one to ignore. How many speed signs or traffic lights for that matter travel at speed. Surely if you are behind a speed sign on a vehicle (or set of traffic lights being transported) and you are doing 50mph, its pretty obvious that its not a static speed sign and can be ignored.
Likewise, wheelie bins, but not sure what effect they have on vehicle behaviour.
I can see it being slightly less straight forward if you pull up behind a vehicle with a speed sign stuck on the back, or transporting a set of traffic lights so they will be static, but tracking the objects and/or position of objects close to a vehicle is probably a clue that these are not valid objects. Unless Tesla cannot tell the difference between a speed sign/traffic light positioned at the back of a vehicle in the middle of a carriage way from those to the side or above.
Hopefully the problem will largely go away when we get single stack and speed signs in adjacent roads can hopefully be seen in the context of position and not just as some discreet visual item with no spatial context.