As of 0.1.243 This now works in the Setters Scenario, but issue still occurs in the VisualStates/Storyboards scenario. Removing references to Setters in Ticket.

Used to include:

Currently, an ImageBrush can't be changed within a Storyboard or Setter

Repro Steps:

1) Create a Project containing a MainPage.xaml
2) Add at least two bitmap images to the Project's directory so that they can be accessed by the Project's UI in the following steps.
3) Introduce a Button Element onto the Page.
4) Right-Click on the Button, navigate to 'Templates', then under 'Button', select 'Create' to create a Button Template.
This will open the button in the Template Dummy Editor (Magenta border around Stage)

5) Select the Border pre-populated in the Button Template, navigate to its Properties, select the 'Background' Property, and select 'ImageBrush', and select any bitmap image.

6) Navigate to the Animation/Visual States tab, and under any of the pre-populated Visual States, select the Border Element, and attempt to have it change Background Image during any of these states.

Observe how the image displayed within the Border doesn't change, and no keyframes are logged to key the image swap.
(The same failure-to-log mechanic also applies within Storyboards)

7) Navigate to the Button's Interactivity/Setters Tab.

8) In the pre-populated IsMouseOver=True Setter, change the Border's Background/ImageBrush to any Image.

9) In the pre-populated IsPressed=True Setter, change the Border's Background/ImageBrush to any second image.

Observe Studio crashing.

Expected Results:
ImageBrush Image Source Properties can be changed on the fly within Storyboards, Setters, and VisualStates just as any other colour Property can.

This is now fixed with r16932.