Okay, now it makes sense. Any item automatically made by Flash and named "tweenX" where X is a number is NOT an normal symbol. I think it was pretty stupid of Macromedia to use this feature, because it causes confusion such as that you are currently experiencing.
Motion tweens are only supposed to be executed using symbol instances. When you try to create a tween with broken shapes and lines, Flash sometimes creates "tween" symbols. These aren't symbols in any normal sense ... they are just instructions for Flash to remind itself what needs moved and where to. Just for the record, "tween" symbols are BAD.
Here's how you SHOULD create a motion tween of a ball bounce:
1. Draw a circle on stage.
2. Select the circle (and its line if it has one) and press F8 to convert them to a symbol. Call the symbol "ball", and check the "graphic" behaviour. Click OK.
4. Make sure the instance of "ball" on the stage is selected, then press F8 to convert it to another symbol. Call this one "bounce" and check the "movieClip" behaviour. Click OK.
5. Double-click the "bounce" movieClip on stage and put a keyframe (press f6) in frame 20.
6. Right-click in frame 1 and select "create motion tween" from the context menu. All the frames in that layer should go blue, and you should have a solid line with an arrow at the right hand side through them.
7. Click in frame 10 and create a keyframe - this should break up the arrow into 2 arrows.
8. Presuming that your ball is going to start at the top of its bounce, select the ball instance in frame 10 and move it down to the required bottom position (try not to move the ball left or right).
9. Adjust easing as reuired (I normally find 100 in on frames 1 and 20, and 100 out on frame 10 works well).
Then test your movie. If you want to change the colour of the ball by making a new "ball" symbol, you will have to duplicate "ball", make the necessary adjustments, then duplicate "bounce", and within the new "bounce" movieClip, swap all the original "ball" graphics with the new ones.
It's a bit awkward, but it's better to do it this way, trust me. If you see a "tweenX" symbol in your library, one of your tweens is not right, and it will cause you no end of problems.