BUG: All posts are assigned for peer review

[JoelWiebe]

Bug

Overview
In the Workspace, when peer reviewing posts from the canvas to a bucket, all posts across the project were displayed as posts to review (including all posts from other buckets or that were removed from the canvas).

To Reproduce
Steps to reproduce:

1. Create posts on the canvas and in multiple other buckets
2. Go to Workflow tool to create a new workflow
3. Create a Peer Review workflow that assigns all posts from the canvas for peer review by one group
4. Go to Workspace as a member assigned to the peer review task
5. See that posts from other buckets are also assigned for peer review even though the source for peer review is the canvas