Flaky button behavior under CS5

programming flash
1

I’m running an app written in CS4 where most of the buttons still work. I have a popup, which goes to a certain frame with buttons on it. The following code is applied in that frame on that MovieClip popup.
This

this.book0_btn.label_txt.text = "speed_: Slow";

works.
This

this.book0_btn.visible = false;

works.

This

this.book0_btn.addEventListener(MouseEvent.MOUSE_UP,changespeed_);

apparently no longer works. Neither does the use of Flash’s suggested target path, or Object(this) or MovieClip(root), etc.