ActionScript 3 :: Object Getting Stuck And Bouncing Back / Forward Rapidly?

I currently have objects populating the screen randomly and bouncing around the stage. The problem is, some of the objects are getting stuck and bouncing back and forth rapidly between two points. How can I prevent this?

Here's how I have the EnterFrame setup:
var ballT = e.target
ballT.x += ballT.vx;
ballT.y += ballT.vy;
if (ballT.x + ballT.width / 2 >= sWidth || ballT.x - ballT.width / 2 <= 0) {
ballT.vx = - ballT.vx;
} else if (ballT.y + ballT.height / 2 >= sHeight || ballT.y - ballT.height / 2 <= 0) {
ballT.vy = - ballT.vy;
}