Steps to reproduce:

1. Create a new search and add the "Due Date" clause.
2. Select "Due in next" 12 hours and not overdue.
3. (BUG) Switch to advanced. Note the JQL is due <= 12h which includes issues which are overdue. The query needs to be due <= 12h and due >= "0" (NOTE: The quotes are important, that is due <= 12h and due >= 0 will not work).
4. Switch back into simple mode.
5. (BUG) Select "Due in next" 12 hours and overdue. This query makes no sense because something cannot be due in the future and overdue.
6. (BUG) Switch to advanced mode. The query is wrong due <= 12h and due >="0". The query should actually be due <= "0" and due <= 12h which will never match anything.