Why is this clip in the way?

I have a program consisting of 8 clips, each at their own depth level on the main stage.
Four of these are clips created in Flash, the others assembled in AS3.

The last of these (created in Flash) sits at level 8, and has it’s y value set to sit it entirely below the stage when I addChild it. This works fine as an HTML-based SWF, but when I create a projector then the main menu bar is initially blocked by an invisible version of the
8th clip - it’s identifiable as that because clicking opens the hyperlink that it carries.

Why is this happening?