Movieclips never garbage collected?

I have Movieclips in my FLA with timelines I use for various things like animation and buttons. I'm using Flash Preload Profiler and see when I instantiate them they always stay in memory. For example I have a pop-window movieclip and I convert one the the clips inside it to a button. This clip has 2 frames, with timeline code on frame 1 just saying stop(). I open it and close it about 50-100 times and according to Flash Preload Profiler running locally (not IOS) every copy is staying in memory. In IOS it crashes consistently on 10-20 minutes of play with no debug error.

Now I've done 2 days of research. I've removed all event listeners on everything. Removed any clips where possible, and nulled everything I can. I've seen it collected a few times, but most of the time its never collected

Am I using the wrong approach, any suggestions? Thanks very much.