Index: modules/queries/src/java/org/apache/lucene/queries/BooleanFilter.java
===================================================================
--- modules/queries/src/java/org/apache/lucene/queries/BooleanFilter.java	(revision 1174729)
+++ modules/queries/src/java/org/apache/lucene/queries/BooleanFilter.java	(working copy)
@@ -35,8 +35,8 @@
  * SHOULD, MUST NOT, MUST
  * The results Filter BitSet is constructed as follows:
  * SHOULD Filters are OR'd together
- * The resulting Filter is NOT'd with the NOT Filters
  * The resulting Filter is AND'd with the MUST Filters
+ * The resulting Filter is NOT'd with the NOT Filters
  */
 public class BooleanFilter extends Filter {
 
@@ -63,19 +63,6 @@
       }
     }
     
-    if (notFilters != null) {
-      for (int i = 0; i < notFilters.size(); i++) {
-        if (res == null) {
-          res = new FixedBitSet(reader.maxDoc());
-          res.set(0, reader.maxDoc()); // NOTE: may set bits on deleted docs
-        }
-        final DocIdSetIterator disi = getDISI(notFilters, i, context);
-        if (disi != null) {
-          res.andNot(disi);
-        }
-      }
-    }
-    
     if (mustFilters != null) {
       for (int i = 0; i < mustFilters.size(); i++) {
         final DocIdSetIterator disi = getDISI(mustFilters, i, context);
@@ -91,6 +78,15 @@
       }
     }
 
+    // to apply NOT filters we need at least some matching docs (res != null)
+    if (res != null && notFilters != null) {
+      for (int i = 0; i < notFilters.size(); i++) {
+        final DocIdSetIterator disi = getDISI(notFilters, i, context);
+        if (disi == null) continue;
+        res.andNot(disi);
+      }
+    }
+    
     return res != null ? res : DocIdSet.EMPTY_DOCIDSET;
   }
 
Index: modules/queries/src/test/org/apache/lucene/queries/BooleanFilterTest.java
===================================================================
--- modules/queries/src/test/org/apache/lucene/queries/BooleanFilterTest.java	(revision 1174729)
+++ modules/queries/src/test/org/apache/lucene/queries/BooleanFilterTest.java	(working copy)
@@ -225,12 +225,12 @@
   public void testJustMustNot() throws Throwable {
     BooleanFilter booleanFilter = new BooleanFilter();
     booleanFilter.add(new FilterClause(getTermsFilter("inStock", "N"), BooleanClause.Occur.MUST_NOT));
-    tstFilterCard("MUST_NOT", 4, booleanFilter);
+    tstFilterCard("MUST_NOT", 0, booleanFilter);
     
     // same with a real DISI (no OpenBitSetIterator)
     booleanFilter = new BooleanFilter();
     booleanFilter.add(new FilterClause(getWrappedTermQuery("inStock", "N"), BooleanClause.Occur.MUST_NOT));
-    tstFilterCard("MUST_NOT", 4, booleanFilter);
+    tstFilterCard("MUST_NOT", 0, booleanFilter);
   }
 
   public void testMustAndMustNot() throws Throwable {
@@ -297,10 +297,10 @@
     
     booleanFilter = new BooleanFilter();
     booleanFilter.add(new FilterClause(getNullDISFilter(), BooleanClause.Occur.MUST_NOT));
-    tstFilterCard("A single MUST_NOT filter that returns a null DIS should be invisible", 5, booleanFilter);
+    tstFilterCard("A single MUST_NOT filter that returns a null DIS should return no results", 0, booleanFilter);
     
     booleanFilter = new BooleanFilter();
     booleanFilter.add(new FilterClause(getNullDISIFilter(), BooleanClause.Occur.MUST_NOT));
-    tstFilterCard("A single MUST_NOT filter that returns a null DIS should be invisible", 5, booleanFilter);
+    tstFilterCard("A single MUST_NOT filter that returns a null DIS should return no results", 0, booleanFilter);
   }
 }