Repro Steps:

1) Create a Page
2) Introduce a 512x512 Rectangle to the Page within the Root Grid.
3) Navigate to the Animation Panel, and select the 'Storyboards' Tab.
4) Click the (+) icon to create a new Storyboard. This will open the Storyboard for edit.

5) Move the playhead to the 1-second mark, and change Fill value of the Rectangle (I changed it from White to Red).
6) Move the playhead to the half-second-mark, and middle-mouse click on the 'Fill' property.

Observe how it wipes the Fill to 'No Brush'. However, observe that it also removed it from the frame at the 1-second mark instead of creating a 'No Brush' keyframe at the half-second mark

7) Ctrl+Z to undo the wiping of the Brush.
8) Return the Playhead to the 1-second mark
9) Change the Rectangle's Render Transform Angle to any value.
10) Middle-mouse click the Angle property field.

Observe that the value is not reset to the default value.

11) Move the playhead to the half-second mark.
12) Middle-mouse click the Angle property field.

Observe that middle-mouse-clicking has not reset the value to the default, and has not keyed a keyframe on the timeline for a value change.

13) Exit the Storyboard view completely, and click on the Rectangle using the Selection Tool (V).
14) Adjust its Render Transform Angle property to any angle.
15) Middle-mouse click the Angle property field.

Observe how it has successfully reset to a default value.

Expected Results: Property Values can successfully be reset to their 'default' values within an animation using the middle-mouse-click shortcut.