This (and any other move by Twitter to restrict unfollowing in bulk) is just an anti-spam measure. Direct marketers follow as many people in bulk as they can w

This (and any other move by Twitter to restrict unfollowing in bulk) is just an anti-spam measure. Direct marketers follow as many people in bulk as they can without being flagged as spam, a small percentage automatically follow them back, everyone else gets bulk unfollowed, repeat. By doing this you can eventually accumulate an account with thousands of followers which you can then pump commercial messages to. The system works but it's a volume game - if you can't automate the process, you can't make enough money for your time. By breaking tools that enable mass unfollowing, Twitter makes the automation harder and therefore fights spam. ManageTwitter almost certainly knows this.