e815 and corded hands-free doesn't 'hang-up" correctly ...

I have a Samsung-brand corded hands-free with the usual button on the mic
part. It does not hang up reliably using that button. Sometimes pressing it
2 or 3 times will do the trick ... sometimes even 4 or 5 presses will not do
the trick. I will hear a dial-tone between some of the click-attempts. The
other person has gone, but I still connected till I open the phone and use
the red hang-up button.

Thanks for any insights,

-RS-