I build was broken and displayed as such.
The next action then was - someone tried to fix it and then started a build. They then had a change of heart, having thought of something and cancelled the build.
The dashboard icon for the individual build should change from the white arrow on green (running/queued build) to a new icon for cancelled. The overall status of the build definition should be taken from the last completed build and should not remain as running, so in this case should change from the large green arrow to the white cross in a red circle.