thank you for your feedback!
Could you, please give us some more information about the issue you have noticed in order to be able to help you to resolve it:
- what value has the setting "Completed tasks retention policy" into the Settings page? If it is 'Manual delete only', please, change it to any other value at the both devices- WP8 and Windows 8 and let us know if there is any change.
Have a suggestion or face a problem - you can use the Ideas & Feedback portal
to submit ideas, feedback and vote for them.