Project teams document assumptions because there's a cost/inefficiency if everyone doesn't operate with them in mind. It's like getting a ride from someone. You agree on the time/place otherwise the whole thing falls apart or gets unnecessarily complicated.
However, it's difficult for project leaders to mitigate the risk of people not communicating obvious assumptions (they're obvious after all and why spend time going through what everyone already knows).
The answer is patience and shared team experience. People/teams without a few projects together should expect opportunities to improve due to missed expectations/assumptions. Being quickly judgmental doesn't strengthen the relationships that are critical to the success of the team.
