Check the 'And'; 'OR'; 'AND-NOT' priorities.

?text=shotton&rule=author_text&bc_1=and&text=semantic&rule=any_text&bc_2=or&text=open&rule=any_text

In this example we are looking for all the documents having ‘shotton’ as string specified to one of the authors' last name and containing the word ‘semantic’ in their title/subtitle, or those ones containing the words ‘open citations’ in their title/subtitle