Stop truncation of shortcodes in custom text fields?

@Milo and @Howdy_McGee had the answer.

I found the section I needed to modify in my functions.php file:

case 'text':
echo '<input type="text" name="', $field['id'], '" id="', $field['id'], '" 
value="', $meta ? $meta : $field['std'], '" size="30" style="width:97%" />',

It was the value field that was getting truncated, so I passed it through esc_attr() as suggested:

case 'text':
echo '<input type="text" name="', $field['id'], '" id="', $field['id'], '" 
value="', esc_attr($meta ? $meta : $field['std']), '" size="30"   style="width:97%" />',

Problem solved.