Snarf Zagyg
Notorious Liquefactionist
In the old days that was a real problem. Mind you, the ignore functionality back then wasn't integrated into the forum software, but was an extension purchased by the site. So I guess it was hard to implement in a seamless fashion.
In Xenforo the functionality is implemented without that bug: you can't effectively shut out people from an entire thread (including all the posts made by others) by being the thread starter and then ignoring someone.
That's one way to look at it.
Another way to look at it is with the current implementation, if you choose to ignore someone, then you cannot see their threads (which is fine), but they can see your threads.
So let's imagine that you have chosen to ignore someone(s) because they constantly crash your threads in an unproductive way (say it's your thread, and you'd like to have a "Magic Item Shoppe" conversation, and the same group of people show up to each time to derail the conversation into why Magic Items Shoppes are terrible, and any game that has them are bad).
Well, in the future, they still will crash the threads you create. The only difference is that now the thread is unreadable ... for you. Which may have an influence as to whether you want to create threads.
Again, there is no perfect implementation. But there is definitely a difference in perspective. The old default was more protective of the people who blocked; the new default is more protective of the people who are getting blocked- because when you block, that makes the experience worse (as you will not see their threads not a bad thing but they will see your thread and can make them unreadable and/or continue the conversation about you knowing that you will never see it.)