In 6.0.3, the Search Pane is set to expand as far as it needs to in order to show the data. This can be problematic for Document and Product searches. You can set the max width in the CSS.
Go to the theme folder and locate the CSS file for the theme.
At the very end, add:
You may change the width to more or less as you wish. at 50%, it will take up only half the screen.