Currently, if in a Storyboard, if you change a value on Property's field, then you undo via Ctrl+Z, the Keyframe will indeed undo in the Timeline, but the value will persist in a permanent fashion for this Element until the Page is closed and re-opened.

The XAML code seems correct for this, with the issue exclusively impacting what is shown in Studio.

Repro Steps:

1) Create a Studio Project containing a MainPage.xaml
2) Introduce a Grid Element to the RootGrid.
3) Introduce a TextBlock to the Grid introduced in Step 2)
4) Set the following Properties on the TextBlock: Vertical Alignment: Centre | Horizontal Alignment: Centre | Font Size: 80

5) Navigate to the Animation Panel, and create a new Storyboard.
6) With the Storyboard created in Step 5) active, select the TextBlock, and navigate to the Transform section of its Properties Panel.
7) Click-and-Drag over any Render Transform property to change its value.
Observe how the TextBlock has transformed on-Stage, and how the Number in the Properties has also changed.
However, note how the field that was adjusted has not been adorbed with a blue colour coding.

8) Press Ctrl+Z to undo the value change
Observe how the TextBlock on-Stage has indeed reverted back. However, also observe how the number in the Properties has not reverted back.

9) Exit the Storyboard to the 'No Storyboard applied' mode., and click on the TextBlock.
Observe how the Properties changed in the Storyboard, which were undone in the Storyboard, are now the permanent Properties of the TextBlock Element.

Expected Results: Changing a Property within a Storyboard only changes it within that Storyboard.