Steps to reproduce:
- Open a page containing a maths formula.
- Select the formula and click 'Edit' in the context menu. Change the formula (alternatively, switch to inline or block display).
- Decide that you made a mistake. Click 'Cancel'.
Your changes are preserved anyway. Pressing 'Cancel' appears to be functionally identical to pressing 'Done'.
Your changes would actually be cancelled. (What exactly is the Cancel button supposed to do, if not cancel your changes?)