From the eyes of BGP:

The Berner is a typical 'shepherd's dog' personality. This personality has a high degree of 'separation anxiety' from its people....anxiety which is not improved by the presence of another dog.

Though they tend to do well in presence of dogs, cats, chickens, rabbits, small children, etc., it is common to find personality changes when raised in the same house with another dog larger than Sheltie size. These changes vary from dogs that become hyperactive in an apparent attempt to secure the position of 'shadow' to their humans, to those that become less participative.
It seems that this kind of dog cannot act as a 'half-shadow',
so it either continues to work hard at retaining that 'whole' position....or appears to give up to the other dog and becomes more shy, retreating, less secure around strangers and strange places, spends more time by itself.

Early 'selection influences' by the cowherd (senn), to choose a dog that had a drive to keep track of him and within voice distance, would fit the model above. When a shepherd needs his dog, he doesn't have time to say "I wonder where the dog went", or "I'll go round up the dog(s)" like a hunter can.

They would much rather wait in the car than be left behind at home while you shop, go to a restaurant, the theatre, a meeting. The car is an extension of you to which they know you will return. It is common to hear that one will often be in the driver's seat if it has fallen asleep. Many of us carry portable shade in the form of space-blankets which can be placed over the roof and windows of the car if there is no shady place to park..