With a sudden move that enraged many of its users last week, Twitter altered the way the social media platform's "blocking" feature worked.
The policy change gave blocked users the ability to see and interact with your tweets, whereas previously, if you had blocked a user, he or she would have been shut out completely from seeing and interacting with your 140 character posts in his or her timeline.
Many in the Twitter community were outraged. "This is a huge and very serious problem for people, like me, who have received repeated rape and death threats on Twitter on a fairly consistent basis," wrote Zerlina Maxwell in a petition on Change.org.
"Twitter is an important means of connecting and communicating. It needs to be a safer place for women and others vulnerable to harassment," San Francisco's Andrew Linstrom commented.
Five hours later, Twitter nixed the change, and reverted the "block" feature to its original setting.
Or so it says.
CNBC has discovered that previously blocked users who visited your profile and clicked "Follow" on your account during the five-hour window are currently able to see your tweets like an unblocked user.
This CNBC reporter took the opportunity during the change to re-follow three accounts that had previously blocked him. While Twitter's vice president of product, Michael Sippey, wrote on the company blog that "any blocks you had previously instituted are still in effect," the tweets from these three accounts have continued to flow into the reporter's main timeline on Twitter.com and the company's official mobile app, although he can no longer interact (retweet or favorite) with them.
"In reverting this change to the block function, users will once again be able to tell that they've been blocked," added Sippey. Except that's not the case: When visiting any of the three profiles, it shows that our reporter is currently following the account.
Another CNBC employee has had a similar experience with an account he followed during the five-hour slot. The tweets from this account that had previously blocked him now display in real time in his timeline.
When asked by CNBC whether users are able to currently see tweets from accounts that have blocked them in the past, a Twitter spokeswoman said the change "was already completed when we announced it." The company may be completely unaware of a loophole that has given stalkers instant access to tweets from accounts that had blocked them in the past.
Twitter didn't immediately respond when asked for comment about such a loophole.
Is the solution a patch on Twitter's side? Do users now need to manually re-block accounts that have re-followed them during the original change, and if so, will they remember the names of all the accounts they've blocked in the past?
Update: It appears as if Twitter has patched the hole. Users who took the opportunity during the small window to follow accounts that had blocked them prior to the Dec. 12 policy change are no longer able to view the tweets of those accounts in their timelines. From the looks of it, the patch was applied Tuesday night. A company spokesman did not immediately respond with comment.
—By CNBC's Eli Langer. Follow him on Twitter at @EliLanger.