This is a strang problem (bug?).
If I perform a motion tween along a curved path, Flash CS4 does not allow to change the curves to "corner point" or "linear" in the motion editor
Here is a video: http://screencast.com/t/ZmI0NmU1Nj
You can. Use the Alt key on the control point in the motion editor.
Great, thank you!
Sometimes, one must have a magic wand to find these little tricks. ;-)