Currently, when entering a Focus Visual Style, many Properties display somewhat erratic behaviour, and some are unable to be modified, and can be found 'snapping' back to their value from before it was attempted to be modified.

Repro Steps:

1) Create a Studio Project containing a MainPage.xaml
2) Introduce a ListBox to the Page, and select it.
3) Expand the 'Styling' Properties Section, open the expander, and next to the 'Focus Visual Style' row, press the (+) to create a New Style.
This will open the Style in the Style's Dummy Editor.

5) Open the 'Foreground' Property, and drag the colour selector in the graph to the upper-right-hand-corner to select a blue.
Observe the Colour Picker 'snapping' back to the far-left.

6) Still with the Colour Picker open, move the selector circle back to the upper-right.
Observe the Colour Picker now respecting the selected value, but generating a XAML error in the process.

7) Close the picker for the Foreground, and open the 'Background' Property, and drag the colour selector in the graph to the upper-right-hand-corner to select a red.
Observe the Colour Picker 'snapping' back to the upper-left.

8) Still with the Colour Picker open, move the selector circle back to the upper-right.
Observe the Colour Picker now respecting the value.

7) Close the picker for the Background, and open the 'Border' Property, and select the 'Solid Color Brush' Tab.
Observe how the tab is non-functional and does not open.

8) Attempt to select any other Tab in the Border's Brush popout.
Observe how no tabs are functional other than the 'No Brush' one.

9) Closed the Brush picker, and attempt to modify the Style's 'Width' value to any number by clicking-and-dragging over the input field.
Observe how the value snaps back to its original value.

10) Now, attempt to modify the Style's 'Width' value to any number by typing it in by hand.
Observe how the field now correctly populates.

10) attempt to modify the Style's 'Margin' value to any number through either value input or click-and-drag over the field.
Observe how the value snaps back to its original value.

11) Attempt to further modify any other Properties.
Observe how most Properties exhibit similar behaviours as above.

Expected Results: A Focus Visual Style's Properties can be changed freely.
If they are in fact not, then the UI should reflect this ability more clearly by greying out/disabling Properties.