When adding a participant to a survey, during attributes mapping :
when the list of attributes in the left column is bigger than the screen height (let's say, when having 50 or more attributes), it is difficult to transfer items from the left column to the middle one, because the item taken from the left column has to be dropped near the top of the middle column.

This requires scrolling while holding the mouse button down.

A better approach would be to be able to drag attributes from the left column to any area of the middle column (which would automatically append the attribute to the bottom of the list of the middle column).