Block preview shows wrong preview image

Description

Steps to reproduce

1. Create an Alloy site.
2. Install ab testing.
3. Navigate to edit cms pages.
4. Select start.
5. Edit the "Alloy plan" block in the bottom left of the screen.
6. Replace the Alloy plan image with another of your choosing.
7. Click publish / Ab Test changes. The image you see in the challenger should be the image you just replaced.
8. Click cancel.
9. Replace the image with a new image.
10. Publish / Ab Test changes.

Expected:
The image in the challenger spot should be the one used in step 9.

Actual:
The image is the one shown in step 6.

Workaround:
Click revert changes and use the image you wanted to use in step 9