I found a plausible explanation in this article:
Here are three examples used:
(1a) The prisoner was hungry and was given a meal.
(1b) ? The prisoner was hungry and given a meal.
(2a) The novel was long and was read over many weeks by the class.
(2b) ? The novel was long and read over many weeks by the class.
(3a) The tree was young and was not climbed by the children.
(3b) ? The tree was young and not climbed by the children.
Here are three examples used:
(1a) The prisoner was hungry and was given a meal.
(1b) ? The prisoner was hungry and given a meal.
(2a) The novel was long and was read over many weeks by the class.
(2b) ? The novel was long and read over many weeks by the class.
(3a) The tree was young and was not climbed by the children.
(3b) ? The tree was young and not climbed by the children.
Comment