_width not changing during tween. is it useless?

I was disappointed to find that I could not use the _width
property of a tweened movieclip instance to know how large
the mc is at a given time.

Am I just not getting something??

A breakpoint in the onEnterFrame() function shows that
_width is always the LARGEST width the movieclip
ever has – not its CURRENT width. In my case the mc is being
made larger and larger, using a tween made in the authoring
environment. The clip starts out tiny and ends up 400 pixels wide,
but the _width property is 400 the entire time!

What gives??

i really appreciate enlightenment!