The new dup was hide while the old title_mc is still there and when click in IS and then back button, no title was there(new and old).
BTW, I try to hide the old title_mc with your code,after going in IS and back from there it generates this error:
the button is being click!
[object backbtn1_45]
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at interactive_fla::MainTimeline/frame1()[interactive_fla.MainTimeline::frame1:17]
at flash.display::MovieClip/gotoAndPlay()
at interactive_fla::MainTimeline/onClick4()[interactive_fla.MainTimeline::frame25:12]
then no button can be click.