Romain Guy write a little info about a ScrollView attribute that is missing  from documentation : android:fillViewport=”true” .

It must be set to ScrollView and has the following efect : when set to true, this attribute causes the scroll view’s child to expand to the height of the ScrollView if needed. When the child is taller than the ScrollView, the attribute has no effect.

Source : http://www.curious-creature.org/2010/08/15/scrollviews-handy-trick/