Calls hang up when placing on hold to answer another call

Hi,

This has been happening to me lately. I was on the phone with a friend, my mom, my boss or anyone and when an incoming call comes in I click hold and answer. Well, it drops my call with the first person and answers the second call. Does anyone else have this issue?

Or another way to explain it...

When person 1 and I are talking person 2 calls me and I press hold & answer option. Once I press it, my phone hangs up on person 1 and picks up the call with person 2. Why does it do this?