Index: boost/spirit/home/karma/numeric/int.hpp
===================================================================
--- boost/spirit/home/karma/numeric/int.hpp	(Revision 76795)
+++ boost/spirit/home/karma/numeric/int.hpp	(Arbeitskopie)
@@ -207,12 +207,47 @@
         template <typename OutputIterator, typename Attribute>
         static bool insert_int(OutputIterator& sink, Attribute const& attr)
         {
-            return sign_inserter::call(sink, traits::test_zero(attr)
-                      , traits::test_negative(attr), force_sign) &&
-                   int_inserter<Radix, CharEncoding, Tag>::call(sink
+          // I have serialized the calls to better follow with the debugger what's going on.
+          bool is_zero = traits::test_zero(attr);
+          bool is_neg = traits::test_negative(attr);
+          // Until here everything seems OK, *attr still has its value.
+          // I can use, e.g., the attribute in a function call.
+          Attribute attr_copy = dummy_function(attr);
+//          bool r1 = sign_inserter::call(sink, is_zero
+//                      , is_neg, force_sign);
+          // After the sign_inserter call, *attr becomes surprisingly zero.
+          // Therefore, I inlined the important code parts to output the sign.
+          if (is_neg) {
+            *sink = '-';
+            // After putting the character into the sink, the *attr becomes zero.
+            // Why??? This happens consistently unimportant whether it's
+            // compiled using g++ or clang++ on Linux or Mac OS X. Is the sink
+            // not correctly constructed and leaks memory?
+            ++sink;
+          } else if (force_sign) {
+            if (is_zero) {
+              *sink = ' ';              
+            } else {
+              *sink = '+';           
+            }
+            ++sink;
+          }
+          bool r1 = true;
+          bool r2 = int_inserter<Radix, CharEncoding, Tag>::call(sink
                       , traits::get_absolute_value(attr));
+          return r1 && r2;
+//            return sign_inserter::call(sink, traits::test_zero(attr)
+//                      , traits::test_negative(attr), force_sign) &&
+//                   int_inserter<Radix, CharEncoding, Tag>::call(sink
+//                      , traits::get_absolute_value(attr));
         }
-
+      
+      // Dummy function for pure diagnostic reasons. It just returns a copy of the attribute.
+      template<typename Attribute>
+      static Attribute dummy_function(Attribute const& attr) {
+        return attr;
+      };
+      
     public:
         template <typename Context, typename Unused>
         struct attribute
@@ -237,7 +272,6 @@
         {
             if (!traits::has_optional_value(attr))
                 return false;       // fail if it's an uninitialized optional
-
             return insert_int(sink, traits::extract_from<T>(attr, context)) &&
                    delimit_out(sink, d);      // always do post-delimiting
         }