Help me understand query syntax of subqueries

[Tigi Scramble]

Any idea why this query returns 0 records:
    "sexual assault" AND (-obama)
while this one returns 1400 ?
    "sexual assault" AND -(obama)


Some debug info:

"sexual assault" AND (-obama), translates to:  +text:"sexual assault"
+(-text:obama), returns 0 records

"sexual assault" AND -(obama), translates to:  +text:"sexual assault"
-text:obama, returns 1400 records

"sexual assault" AND obama,    translates to:  +text:"sexual assault"
+text:obama, return 53 records

(-obama), translates to: -text:obama, returns 716295 records
-(obama), translates to: -text:obama, returns 716295 records


I am using Solr 1.4
qt:standard
QParser:LuceneQParser

Thanks,
Mis