When a project is disabled, still it can execute a build.
In the eXtreme Feedback panel it is shown as not building.

The reason:
hudson.model.AbstractProject.getIconColor()
public BallColor getIconColor()
{
if (isDisabled())

return super.getIconColor();
}

This can be changed to:

BallColor normalColor = super.getIconColor();
if(isDisabled())
{
if(normalColor.isAnimated())

return BallColor.DISABLED;
}
return normalColor;

We use disable project to let a project finish his job and then take action on that job and prevent a next build is started.
The eXtreme feedback panel does not help us right now to see if the job is finished.