Most Helpful Guy
You typically block someone because they annoy you, but if you unblock them, it's because you're curious and want to still be able to stalk their profile. This is what I'm guessing your ex is doing.
Most Helpful Girl
Yes, when I had a Husband out in Egypt, A million times Over.. Block and Unblock. It became a "Full Circle Problem Pattern."
However, like any Media Site, Many of us 'Block.' I myself have Done this at times, where I will give Someone a Second Chance, but when I Realize it isn't Going to Work... I Pushed a Button again to Re-block, where I then Moved on.
Good luck. xx