contentbylabel operator=AND performs like an OR

Steps to reproduce the problem:

1. Create a page and set the labels:a
2. Create a page and set the labels:b
3. Create a page and set the labels:a , b
4. Run this macro :

   {contentbylabel:a,b|operator=AND|maxResults=10}

   • This works fine. It returns the page where label "a" ,"b"
5. Run this macro :

   {contentbylabel:a,c|operator=AND|maxResults=10}

   • This macro should not return any results as there is no page with the label "a" and "c"
   • However, it fails and returns all the pages with the label "a" even though there is no page with the label "c"