By "Bounces up and Down", do you mean this:
The content of the screen drops down and about a third of the top of the screen is blank.
When you press the home button or any icon, the content moves back to the top of the screen.
If this is what you are seeing, it is intentional. It is meant as a way for you to be able to easily reach the icons at the top row of the screen.
Double tap the home button. Do not press the button, just lightly tap it.
All the content should drop down.
Pressing the home button or any icon will shift the content back up again.
This is a new feature designed for the larger screens in the 6 and 6+.