I've created a layer that represents a modal dialog. On that layer I've added a tab control with 3 tabs, and each tab has various controls.
The layer is shown when an icon is clicked on the main screen, and is positioned using the page absolute positioning.
If the layer is not EXACTLY placed on the screen in design-time where it will be placed at runtime, then flipping to another tab causes the contained controls to be displayed in their design-time positions.
To summarize, the page-absolute positioning transformation is not being applied to contained controls.