Complete stop, then bounces front foot: Why not a balk?

[Coach.HS]

The pitcher comes set, complete stop, then bounces (taps) one or more times with his front foot prior to his delivery.

It's not common. But we see it occasionally.  It's tough on basestealers.

Why isn't each tap of the foot considered the start of the delivery?

Below is an example from MLB.  The commentator says, "Three times his heel comes off the ground after his hands come set."  That's what I see too.

Would you balk this under Fed. rules? 

(Here's a gif and video of the same sequence).

 

https://imgflip.com/gif/k5q80

 

http://m.mlb.com/video/v7047233/mlb-network-examines-whether-betancourt-balked

 

Thanks!

[noumpere]

What about jump throws to 1B?

Legal, subject to the same requirements of any other throw.  Considered to be a move from the rubber.