The EDIT mode times out after a set period of time.
If you have not completed the tariff adjustment and hit save, it forgets what change you have made when it times out and you need to start again.
To solve this, simply add the tariff (price) in smaller chunks:
- Enter EDIT mode
- Increase the tariff by 10c
- Exit EDIT mode
- Re-enter EDIT mode and increase the tariff further.