ACS HTTP REST Querying Posts Object for Users

All,

I am making a rest call to ACS, trying to pull those posts create by friends. I am passing in the array of users with the following call:

https://api.cloud.appcelerator.com/v1/posts/query.json?key=xyzxyzxyzxyz&query='where={"user_id":{"$in":[friendIDarray]}}'

I don't have any records created by friends, so I expect my array of posts to be empty. All I get back is my posts. What is the expected behavior, and is my query formatted correctly?