Repro Steps:

1) Create a Page
2) Introduce 2 Rectangles to the Page's RootGrid, each of dimensions of 512x256.
3) One-at-a -time, right-click on each Rectangle, and convert each one to a Path via its context menu, by navigating to 'Path'->'Convert to Path'.
4) Select one of the two rectangles, and in its Properties, navigate to the Render Transform section, set its Origin to Centre, and set its Rotation to 30°.
5) Right-Click on the rectangle that was Render Transform Rotated, and from its context menu, navigate to 'Path'->'Flatten Transform'.

6) Equip the Selection Tool (V), grab one of the adorners of the non-flattened rectangle, and click-and-drag it in any direction.

Observe how the non-flattened rectangle Path changes its size with adjustments in the adorner position.

7) With the Selection Tool (V) still equipped, grab one of the adorners of the flattened rectangle, and click-and-drag it in any direction.

Observe how the flattened rectangle Path that was rotated changes its Bounding Box dimensions rather than its Path dimensions like the non-flattened version does.

Expected Results: The same adorner functionality functions the same for both Flattened and Non-Flattened Paths, since a 'Flattening' should essentially just be baking in the changes made to the Path Points during a Render Transform.