(This applies to the Scrum board's burndown chart.)

When someone logs work and makes a huge mistake with the remaining estimate - e.g., entering days instead of hours (due to the default time unit) -, the burndown chart's remaining estimates line will show a spike. When correcting the mistake by editing the work log entry and fixing the remaining estimate, the spike should be removed, but it is not. For an example, see the attached file "burndown.png" and for the culprit, see "logged hours.png".

These spikes can get so high that the burndown chart is no longer readable, see "burndown2.png".