I'm the co-worker in question. I wasn't using fromTo before out of sheer ignorance, but I am now and oddly, the problem seems to be fixed.
I'm still somewhat curious as to what went wrong with my old approach in the new version, so here's a rough snapshot of the old and new code:
Old:
var myTimeline:TimelineLite = new TimelineLite( { useFrames: true } );
myTimeline.add( [TweenLite.delayedCall(0, subInGraphic, [graphic2]), TweenLite.delayedCall(0, graphic2.gotoAndStop, [1]) ]);
myTimeline.add( [TweenLite.delayedCall(0, graphic2Sound.play), TweenLite.to(graphic2, graphic2.totalFrames, { frame: graphic2.totalFrames, ease: Linear.easeNone } ) ]);
New:
var myTimeline:TimelineLite = new TimelineLite( { useFrames: true } );
myTimeline.add(TweenLite.delayedCall(0, subInGraphic, [graphic2]));
myTimeline.add( [TweenLite.delayedCall(0, graphic2Sound.play), TweenLite.fromTo(graphic2, graphic2.totalFrames, { frame: 1 }, { frame: graphic2.totalFrames, ease: Linear.easeNone } ) ]);
Thanks!