Ouch, sorry for the snag! I can confirm that renaming mockups from the editor is causing this bug, we’ll fix it!
In the meantime, you can rename mockups from the Project page or Single Mockup page to avoid the issue.
While I agree this could be useful, this probably won’t be implemented because we are moving away from the BMML format in the next major web version (already in private beta). For this reason, the easiest way to achieve this is:
- Export the Mockup to XML
- Open it in a text editor and make your changes
- Delete every element in the mockup
- Import the XML
More details about the XML option can be found here if needed.
Hope this helps. Thanks for the bug report!