Instance names not being detected/disappearing.

I've got something funny going on when I export my Flash file.

http://www.deadringerart.com/ugly-gi.../trouble01.jpg

Look at the "button" layer. Each keyframed object on that layer has the instance name "buttonOverlay". (The two exceptions are frames 6 and 29, in wich the "blur" layer objects get said instance name.)

I'm trying to resize and reposition a Movie Clip based on the size and position of "buttonOverlay." This works fine up until frame 29. After that, the player can't find any instance named "buttonOverlay." I wrote a trace and it says:

"In frame 2, x=2.65
In frame 3, x=1.3"

...and it continues in a similar fashion until...

"In frame 28, x=-10
In frame 29, x=
In frame 30, x=
If frame 31, x="

and on until I loop it back around to finish at Frame 25, in which it once again starts reading "buttonOverlay"

"In frame 25, x=3.2"
...and stop.

It does the same thing with the y value. Why does it suddenly stop reading "buttonOverlay" after a specific frame? I've quadruple checked to make sure there actually is a "buttonOverlay" in each frame, and that it's spelled the same.