Another closely guarded question

[fshrake]

A1 is being closely guarded by B1. A2 sets a screen on B2 and A1 dribbles around the screen with B1 still guarding him and still within 6 foot.
In this example I have been told to drop the count when A1 goes around the screen and restart it. In the above example B2 is always within 6 foot so why would I stop the count at the screen ?