It wasn't that bad. It just made that ripping sound that Velcro makes when you pull it apart. It didn't stop him walking for a few steps and then falling over again.
I had to bring him downstairs and shut the hall ddoor. I could foresee that he'd do a melodramatic fallover at the top of the stairs, and not be aware of the consequences.
He's now walking around and falling over around me.
I hope this phase doesn't last long.