If you have a user on your ignore list, then you are still able to see threads they've opened, you are just not able to see their posts in this thread anymore.
So it's not enough to ignore a user, if you don't want to see the threads anymore as well, you have to ignore the thread as well by clicking on > thread tools > ignore this thread and after that the thread is not visible for you anymore (but sure that means that you will have to open the thread at least for once to be able to ignore it)
Not sure if it would be possible to have the option to ignore all threads from specific users automatically (if that is what some posters want)
If you want to stop to ignore a thread you have to go to your user cp > settings & options > Ignored Threads > stop ignoring this thread