Customer encountered problems with RichText editor. After undoing some changes (using Ctrl+Z / Cmd+Z) all the images which were embedded using UDW disappear.

Steps to reproduce:
1. Create new content which contains RichText field, e.g. Article.
2. Type some text.
3. Attach an image using embed or image widget.
4. Hit "undo" keys combination: Ctrl+Z / Cmd+Z.

Result:
A small rectangle is shown instead of an image (see attachment).

Note 1:
This issue applies only to content which was embedded using UDW (either existing one from the library, or a new one which was uploaded using "Create" tab). Problem doesn't show up when attaching image via drag&drop.

Note 2:
In v2 behaviour is a bit odd: images disappear, the small rectangle shows up but immediately after that images appear once again.

Note 3:
After publishing the article, images are renderred correctly.