ActionScript 3.0 :: Shape Displays In One Part Of Program, But Not In Other

I have multiple simple audio players displayed on the screen, each contained in an HBox. Each audio player has a Waveform, a Container that displays a waveform Shape that is drawn from samples.

The issue I've been having is that in one part of the program, where multiple audio players are just added to a tab from top to bottom, the waveform displays fine, as well as the bar that tracks the current position of the audio playing (a child of WaveForm). However, in the main part of the interface, where audio players are indented such that each audio player has a visible "child" audio player that can be expanded/hidden, the WaveForms don't display at all.

The strange thing is that these sound player objects are being created by the main tab where the waveform isn't displayed, and are occasionally sent to the other tab where the waveform works - they're the exact same objects, and the WaveForm objects retain the same parameters and visibility etc when they're passed, they just aren't drawn. In the tab where they aren't being drawn, the only additional parent graphical component is an HBox containing all of the sound players - I can't figure out for the life of me if I'm missing some sort of parameter or what.