Same. I'd got recent (probably simply out of date) incorrect information about this.
Edit: Billd91's post above seems to at least somewhat contradict this. Would anyone care to elaborate?
You are ignoring UserX. You have enabled 2-way ignore (hiding posts both ways) .
You start a thread in the D&D forum. UserX will see that thread when they view the D&D forum as if it were a normal thread. UserX will see your first post in the thread. They can respond to it, and other people in the thread. They will not see subsequent posts by you in the thread.
UserX starts a thread in the D&D forum. You will not see that thread when you view the D&D forum, and it is likely you don't know the thread exists. You will still see that thread if it becomes the most recent post on the Forum List, and a few other places. You can still post in that thread if you navigate to it. You will still get notifications about that thread if you follow it or someone mentions you in it. UserX will not see your posts in that thread. You will not see posts by UserX in that thread (including the first post).
With this form, no one is completely blocked out of a thread and unable to respond to it due to ignore settings. This is the way things work with the current forum software, but it's not how it has always worked in the past.
Hope this clears things up.
FWIW, I prefer using 2-way ignore. Some people are on my ignore list just because I find them annoying, or for the mental health reasons mentioned above. It wouldn't be a big deal if they could see my posts. But there is also a (very) short list that I believe are straight up trolls that have just learned to be polite enough to skirt the rules here. I absolutely do not want those people able to see my posts. There are definitely a couple of bad seeds that would take advantage of that and intentionally misrepresent what people ignoring them say, knowing that their target couldn't respond.
