Hi,
Well, I think the issue is that when you press the button the first time it sends "A" and the receiver responds by setting the PWM outputs etc. But when you release the button the sending PIC does nothing, thus the receiver sits at the SERIN command waiting for something to come while the PWM outputs are active in the background.

You need to change it so that sends sends "A" when the button is pressed and something else when it's released.

At least that's what I think is going on.

/Henrik.