Displacement map disappears when MC too large

Hi

I have a displacement map targetting an mc that is placed on the stage. My problem is that as soon as the mc is over a certain height the displacement map disappears.

For instance, when my mc is 1977px high the displacement map works, but as soon as I add any more images to it and take it over that height the displacement map disappears. (the target mc is static)

Does flash have a maximum width and height for images even when placed off stage? The stage dimensions are 604 x 409 and the tall mc is running off the stage.

Does anyone know why the displacement map would fail once the mc was too long?