The following procedure shows the problem:

1. Open the Pages app
2. Click on one
3. Click on Move page
4. Notice the layout
5. Click on a page
6. The correct layout is shown

However, a slight layout alteration in MGNLUI-3905 (in progress) reveals that the problem is general and not limited to the Move dialog, cf. the attached screenshots. On the current demo, the problem is limited to the gray, half-visible area of the Move dialog. Only with the refactoring of the buttons do we also see the buttons popping from the window just after the transition, going back to their correct place when some action refreshes the view.

Update with MGNLUI-3905 merged: the status there is that the CSS zooming breaks the layout. apchelintcev looked at it and suggested a proper loading mechanism should be implemented sometime in the future. See MGNLUI-3905's diff to overlay-admincentral.scss for more details. For the time being, though, everything seems to work just fine as is.