sql_delete.cc:

  Fix bug: if a DELETE failed in a FOREIGN KEY error and it had already deleted some rows, then MySQL did not roll back the failed SQL statement, and also wrote it to the binlog

sql/sql_delete.cc

@@ -145,7 +145,12 @@ int mysql_delete(THD *thd, TABLE_LIST *table_list, COND *conds, ORDER *order,
       else
       {
 	table->file->print_error(error,MYF(0));
-	error=0;
+ 	error=1; /* In < 4.0.14 we set the error number to 0 here, but that
+		 was not sensible, because then MySQL would not roll back the
+		 failed DELETE, and also wrote it to the binlog. For MyISAM
+		 tables a DELETE probably never should fail (?), but for
+		 InnoDB it can fail in a FOREIGN KEY error or an
+		 out-of-tablespace error. (Comment by Heikki July 7, 2003) */
 	break;
       }
     }