Runtime generated sprites sometimes stick to zero x and y coordinate...ideas?

I have bug in an actionscript 3.0 mp3 player i’ve written where all of the graphics (ui) are generated by actionscript at run-time but occasionally they all get stuck on the zero x and y coordinate making the program difficult to interface with. I set the coordinates of the sprites with some math: stage.stageWidth/2 and stage.stageHeight/2 for instance.

I don’t know in which particular browsers this tends to be a problem but it has happened in Firefox and IE, though not consistently, which is really confusing. Has anything similar happened to anyone and might they please share their insight? Is it my fault or someone else’s (i.e. - adobe, ms, mozilla, etc.)?

Many thanks to any who care to share their experience.