I am not a teacher.
But isn't one definition of a participle a word formed from a verb and used as an adjective? If so, then in 1) "broken" is a participle behaving as an adjective.
You say 2) is in the passive voice, but "broken" could just as easily be predicative. The way I automatically understood 2) was that "broken" was an adjective.
The window was broken.
The window was dirty.
Student or Learner