Seems you don't know what is "Using EAD"

For every employment, you have to file I-9, that's the form your HR/Payroll decide your tax status. For H1b, you fill in the H1b info. For using EAD, you need to file a new I-9, with EAD info. So there is no such thing as automatically using EAD. You have to physically provide your EAD copies to your HR to use it.

Thus, most H1 Status holders, after using AP, come back to the same company and continue to be H1, because they do NOT use his/her EAD.

Actually, if you have a H1b visa (also filed 485), DO NOT leave without an AP, otherwise your I485 will automatically being dismissed if you leave US without AP.