A quick rundown:
1) If a user is ignored: Threads/posts of that user are hidden. (Alerts don't come through).
2) If a user is muted within a thread: Their posts are hidden (Alerts still come through).
3) If a user is muted forum-wide: The thread is visible, but their posts and any interactions with that person by other users are not. (Alerts still come through).
4) If a user is blocked: The thread is visible, but your posts are not, nor are any interactions between you and other users. Their posts and interactions are also not visible. (Alerts still come through).
At no point in any of the above is a user prevented from posting/participating within a thread. The ignore function is a choice by the user, so they're not prevented from participating. Unfortunately, the threads are hidden by the software by default, and I'll have to figure out how to override that.