Two questions regarding H-1 and AP

First question --

Is it OK to go back to apply for H-1 while H-1 is pending for renewal?

Second question --

Everyone says that one can keep H-1 status after using AP if he doesn't change the current job. My employer has a definite asnwer to that --> H-1 will be invalid once AP is used. My question is how the employer knows whether or not I use AP. The only evidence is the stamp on the I-94, right? Do I have to give the I-94 copy to the employer after coming back to work?