Select Auto-close -fill -outline -
select your colour for fill and outline and
draw your freehand-shape.
If you like to change the colour afterwards:
Select Shape-Tool - select your shape
and change the fill- and outline-colour.
If you've already got a shape, find the 2 points which represent the end of the line and link them together by moving them close to each other and tapping the [Space] bar. It should close the shape, meaning you should be able to fill it successfully.
I have the same problem, and none of the answers help me: I want to fill a shape by placing an image shape on top of a Moho shape, and it always ruins the black edges that I want. Any other ideas than the ones posted?
Remove the fill of the vector shape and place the image layer behind the vector layer might be a solution. And if you need that fill, sandwich the image layer between two vector layers (fill at the bottom and outline at the top).