Localtoglobal kinda goes bonkers on me

Does anyone here know of a built in limitation to the “localtoglobal” function what would cause something like this:

I am trying to build a ZUI (zooming user interface). I have tackled many of the problems thus far, but here is a totally unexpected one. I have the main content nested within a MC that is then nested within ANOTHER MC on the stage. The reason for this is so that the first nest can be used to move the content, and the other to scale it. This way the two calculations dont interfere.

Here is the wierdness. When the _scale of the top level nest gets to about 2200, then the localtoglobal function i am using to calculate and recalculate the position of everything starts returning increasingly varied results. Oddly enough, only the x value starts wobbling. The y value keeps returning as it should!

Does this sound even VAGUELY familiar to any of you?