Given UserStory A (effort 10), UserStory B (effort 5) and UserStory C (effort 5)
And backlog organization:
Release 1.0
|-- UserStory A
|-- UserStory B
|-- UserStory C
|-- Sprint 1
| |-- UserStory A
| `-- UserStory B
|-- Sprint 2
`-- UserStory C
The Release effort should 20 (10 + 5 + 5). However, there is a bug and stories are counted twice and the effort displayed is 40.
This also affects the burndown.