Description
Burndown chart occasionally displays negative remaining values.

Steps to reproduce

• Create a story with one task with original estimate of 2h
• start sprint
• move task "in progress"
• log 1h using TEMPO
• log 5h using TEMPO
• Change remaining estimate to 2h using the detail section of the work tab of the greenhopper board
• log 1h using TEMPO

Result
The burndown chart temporarily shows -1h remaining:

The burndown detail table incorrectly shows some backdating, which did not happen:

It seems to me that Greenhopper somehow things that the last work log happened before the editing of the remaining hours which is not the case.

Expected result
No negative remaining values anywhere. No display of backdating. Display correct order of events.