Blocked Sites was one of the coolest features Google added to their search engine platform.
Users got the ability to completely remove domains that consistently gave them bad results.
They could add as many as 500 domains to their own personalized block list that is saved in their accounts.
But this feature has been buggy to say the least. Google Search support forums have enough threads from users who have noticed the same.
Google continues to ignore the blocked domains and web pages from them would appear on your result pages.
We believe that this is a result of the major changes Google is implementing on their entire platform which is hurting these smaller features.
Google would eventually fix this problem but until then you have few choices available to you.