ActionScript 3.0 :: Incredible, Ridiculous Video Lag When Using Seek()?

I'm working on development of a medical training app and have come across a stumbling block I can't work out. I'm using FlashCS5, and AS3.Basic setup is this:

- 1 flvplayback with an H.264 MP4 loaded into it, stock controller

- 1 standard UILoader with a jpeg put into it

The jpeg still image is a sideview of a medical image, and the idea is that the user can move their mouse over this image and move the corresponding movie to a certain timecode. The full width of the image maps directly to the length of the movie clip, i.e. if you put your mouse on the very left of the still image, you are at 0 seconds of the movie, all the way on the right will be 49 seconds.

So, attached to my UILoader I added a simple routine that gets the mouseX, does some basic math to determine how far into the movie we should go, and sets the movie to that time.The problem is that using playheadTime, seek(), or seekSeconds() gives me incredible lag. You can move the mouse on the still image and the output window shows instantaneous reporting of the proper calculated time, but the movie itself might take 5-10 seconds to actually move to that time.

The movie has been rendered out using the CS5 Media Encoder and has a keyframe every 1 sec.Here is a link to a screen capture I did to show the problem. As you can see, using the standard controller is pretty responsive, but my other method is unusable. This happens locally as well, with the movie being fully loaded instantly.

h t t p://cl.ly/2gZY (1MB, quicktime)

Partial code, very basic:

ActionScript Code:
screenImageView.addEventListener(MouseEvent.MOUSE_MOVE, pullbackJump);
...
public function pullbackJump(e:MouseEvent):void {

[code].....