5 month gap between H1B termination and extension start date

The H1B at my current employment ends on June 30, 2016. My new employer has filed for an H1B extension with the start date of December 1, 2016.

Assuming that my application is pending/approved, is it Okay to stay in US or should I leave US as soon as my current H1B is terminated?

Thanks for answers

It is not ok to stay and work in US if they are asking for a start date in future. Had they asked for a start date of July 1, you could have stayed but not like this.

What’s the reason for break in employment?

Thanks for the answer. The reason is disagreement at workplace. I am thinking about resigning from my job.