Twitter had to backtrack after a user revolt in regard to the blocking feature. Twitter temporarily enabled a blocked Twitter user to view or tweet the user that blocked them.
Blocked users would still be able to see your tweets while logged in and continue to follow you on the service. This could allow abusers to continue to monitor your updates on the network. Fortunately, Twitter now lets you become invisible to blocked users again.
“We have decided to revert the change after receiving feedback from many users ? we never want to introduce features at the cost of users feeling less safe. Any blocks you had previously instituted are still in effect,” stated Twitter VP of product Michael Sippey in a blog post.