If I get the page indicating that my edits conflict with a newer version (heading "A newer version exists"), clicking the "save" button can result in the content being replaced by a whole slew of %xx codes.
INSTRUCTIONS TO REPRODUCE:
The following steps are the simplest way I know to reliably reproduce the problem:
1. Create a link to a non-existent topic, click on that link.
2. Choose "Edit this page" and enter some text. Save.
3. When the updated page is displayed, click "Edit this page" again, and add to the text. Save again.
4. This time, hit the back button to return to the editing page with all the latest text.
5. Now, add some more to the page and then save it.
6. You will get the "A newer version exists" page. See that the proposed changes are exactly what you want, and click "save"
7. The next page that comes up has all the hex codes. (In the example I just did to verify these steps, I got the following contents...)
I have followed these steps twice to reproduce the problem.