Edit-Tab "forgets" past changes

Under certain conditions the "Edit"-Tab for editing Wiki pages does show an outdated version of the edited page. The problem only concerns the "Edit"-Tab, not the "Show"-Tab, which is showing the latest alterations.

The bug can lead to serious data loss. If a user does not recognize the wrong text and saves the the page, the "forgotten" changes will be lost. Therefore further changing an affected page is not possible anymore without risking data loss.

The problem occurs always once the edit Tab gets canceled in any way (e.g. by pressing cancel, changin to the "Show"-Tab, closing the Browser-Tab).

Easy to reproduce:

( 0) Create a new Wiki page and save the page)

1. Go to Edit-Tab

2. Cancel Edit Tab (e.g. by clicking the Cancel-Button)

3. Go to Edit-Tab again, change the text, save

4. See the changes in the "Show"-Tab

5. Go to Edit-Tab again and watch the change be missing

The bug stays on affected Wiki page further. So any future change will be "forgotten" by the Edit-Tab as well.