Advanced syntax is turned on and there is no any "unusual" characters.
Same happens example with http://www.bbc.co.uk/go/rss/int/news/-/ ... a_pacific/
- there is 13 results with search "China" (Advanced syntax is off) and
- there is 0 results with search "NOT China" (Advanced syntax is on)
I can send some hardcopies of screens and settings by email, if needed.