If you are having some odd or inexplicable issues (like an extra empty note being added / displayed, unable to delete or add note etc.) try this first:
- Delete all the ‘reminders / notes’ you added.
- Right-click The Reminder speed dial, and click Uninstall to remove The Reminder extension.
- From the Opera menu (top-left corner), select Settings -> Delete Private Data … .
- In the Delete Private Data window, click on Detailed Options.
- Now make sure that Delete entire cache, Delete persistent storage and Delete plug-in data are checked.
- Click on the Delete button.
- Exit (close) Opera.
- Start (open) Opera again.
- Now reinstall The Reminder extension again from https://addons.opera.com/en/extensions/details/the-reminder/ .