video_image thumbnail gets replaced on node update

The image associated with a video (when using video_image module) gets replaced under the following circumstances.

1. Create video node A, and attach image
2. Create new video node B, and attach image
3. Edit video node A

Now, video node A has the image from video node B associated with it.

The reason for it is the session variable that indicates that an image was uploaded never gets cleared when no image is associated.