If you are in the conversation area and a friend is writing a message, the area does not scroll down automatically. You can see the reply / message only when you scrol down or the page is updated.
Look Photo...
This is the default behavior. Why? When we were revamping this, we tried scrolling up to read some of the older messages but when a new message arrives, it automatically scrolls down and it is pretty annoying.
Therefore we disabled the auto scrolling effect to avoid these type of annoyance.