diff --git a/mysql-test/r/cast.result b/mysql-test/r/cast.result
index c1af92c5f8d..dd61396e485 100644
--- a/mysql-test/r/cast.result
+++ b/mysql-test/r/cast.result
@@ -439,3 +439,16 @@ HOUR(NULL)	MINUTE(NULL)	SECOND(NULL)
 NULL	NULL	NULL
 DROP TABLE t1;
 End of 5.0 tests
+#
+#  Bug #44766: valgrind error when using convert() in a subquery
+#
+CREATE TABLE t1(a tinyint);
+INSERT INTO t1 VALUES (127);
+SELECT 1 FROM
+(
+SELECT CONVERT(t2.a USING UTF8) FROM t1, t1 t2 LIMIT 1
+) AS s LIMIT 1;
+1
+1
+DROP TABLE t1;
+End of 5.1 tests
diff --git a/mysql-test/r/func_concat.result b/mysql-test/r/func_concat.result
index 7e7c163716e..75b4888fbb2 100644
--- a/mysql-test/r/func_concat.result
+++ b/mysql-test/r/func_concat.result
@@ -89,3 +89,34 @@ c1	c2
 	First
 DROP TABLE t1;
 # End of 5.0 tests
+#
+# Bug #44743: Join in combination with concat does not always work
+#
+CREATE TABLE t1 (
+a VARCHAR(100) NOT NULL DEFAULT '0',
+b VARCHAR(2) NOT NULL DEFAULT '',
+c VARCHAR(2) NOT NULL DEFAULT '',
+d TEXT NOT NULL,
+PRIMARY KEY (a, b, c),
+KEY (a)
+) DEFAULT CHARSET=utf8;
+INSERT INTO t1 VALUES ('gui_A', 'a', 'b', 'str1'),
+('gui_AB', 'a', 'b', 'str2'), ('gui_ABC', 'a', 'b', 'str3');
+CREATE TABLE t2 (
+a VARCHAR(100) NOT NULL DEFAULT '',
+PRIMARY KEY (a)
+) DEFAULT CHARSET=latin1;
+INSERT INTO t2 VALUES ('A'), ('AB'), ('ABC');
+SELECT CONCAT('gui_', t2.a), t1.d FROM t2 
+LEFT JOIN t1 ON t1.a = CONCAT('gui_', t2.a) AND t1.b = 'a' AND t1.c = 'b';
+CONCAT('gui_', t2.a)	d
+gui_A	str1
+gui_AB	str2
+gui_ABC	str3
+EXPLAIN SELECT CONCAT('gui_', t2.a), t1.d FROM t2 
+LEFT JOIN t1 ON t1.a = CONCAT('gui_', t2.a) AND t1.b = 'a' AND t1.c = 'b';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	index	NULL	PRIMARY	102	NULL	3	Using index
+1	SIMPLE	t1	eq_ref	PRIMARY,a	PRIMARY	318	func,const,const	1	
+DROP TABLE t1, t2;
+# End of 5.1 tests
diff --git a/mysql-test/t/cast.test b/mysql-test/t/cast.test
index 50865215944..8e60d548c2f 100644
--- a/mysql-test/t/cast.test
+++ b/mysql-test/t/cast.test
@@ -269,3 +269,18 @@ SELECT HOUR(NULL),
 DROP TABLE t1;
 
 --echo End of 5.0 tests
+
+--echo #
+--echo #  Bug #44766: valgrind error when using convert() in a subquery
+--echo #
+
+CREATE TABLE t1(a tinyint);
+INSERT INTO t1 VALUES (127);
+SELECT 1 FROM
+(
+ SELECT CONVERT(t2.a USING UTF8) FROM t1, t1 t2 LIMIT 1
+) AS s LIMIT 1;
+DROP TABLE t1;
+
+
+--echo End of 5.1 tests
diff --git a/mysql-test/t/func_concat.test b/mysql-test/t/func_concat.test
index f2aa0d004e5..1c7e5823fb2 100644
--- a/mysql-test/t/func_concat.test
+++ b/mysql-test/t/func_concat.test
@@ -78,3 +78,37 @@ SELECT * FROM t1 WHERE CONCAT(c1,' ',c2) REGEXP 'First.*';
 DROP TABLE t1;
 
 --echo # End of 5.0 tests
+
+
+--echo #
+--echo # Bug #44743: Join in combination with concat does not always work
+--echo #
+CREATE TABLE t1 (
+  a VARCHAR(100) NOT NULL DEFAULT '0',
+  b VARCHAR(2) NOT NULL DEFAULT '',
+  c VARCHAR(2) NOT NULL DEFAULT '',
+  d TEXT NOT NULL,
+  PRIMARY KEY (a, b, c),
+  KEY (a)
+) DEFAULT CHARSET=utf8;
+
+INSERT INTO t1 VALUES ('gui_A', 'a', 'b', 'str1'),
+  ('gui_AB', 'a', 'b', 'str2'), ('gui_ABC', 'a', 'b', 'str3');
+
+CREATE TABLE t2 (
+  a VARCHAR(100) NOT NULL DEFAULT '',
+  PRIMARY KEY (a)
+) DEFAULT CHARSET=latin1;
+
+INSERT INTO t2 VALUES ('A'), ('AB'), ('ABC');
+
+SELECT CONCAT('gui_', t2.a), t1.d FROM t2 
+  LEFT JOIN t1 ON t1.a = CONCAT('gui_', t2.a) AND t1.b = 'a' AND t1.c = 'b';
+
+EXPLAIN SELECT CONCAT('gui_', t2.a), t1.d FROM t2 
+  LEFT JOIN t1 ON t1.a = CONCAT('gui_', t2.a) AND t1.b = 'a' AND t1.c = 'b';
+
+DROP TABLE t1, t2;
+
+
+--echo # End of 5.1 tests
diff --git a/sql/item.cc b/sql/item.cc
index 8a8c3610198..62c8bfa3043 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -4873,7 +4873,10 @@ int Item_null::save_safe_in_field(Field *field)
 /*
   This implementation can lose str_value content, so if the
   Item uses str_value to store something, it should
-  reimplement it's ::save_in_field() as Item_string, for example, does
+  reimplement it's ::save_in_field() as Item_string, for example, does.
+
+  Note: all Item_XXX::val_str(str) methods must NOT rely on the fact that
+  str != str_value. For example, see fix for bug #44743.
 */
 
 int Item::save_in_field(Field *field, bool no_conversions)
diff --git a/sql/item_strfunc.cc b/sql/item_strfunc.cc
index 501b7e85080..a3140b4db64 100644
--- a/sql/item_strfunc.cc
+++ b/sql/item_strfunc.cc
@@ -2706,8 +2706,15 @@ String *Item_func_conv_charset::val_str(String *str)
   DBUG_ASSERT(fixed == 1);
   if (use_cached_value)
     return null_value ? 0 : &str_value;
-  String *arg= args[0]->val_str(str);
+  /* 
+    Here we don't pass 'str' as a parameter to args[0]->val_str()
+    as 'str' may points to 'str_value' (e.g. see Item::save_in_field()),
+    which we use below to convert string. 
+    Use argument's 'str_value' instead.
+  */
+  String *arg= args[0]->val_str(&args[0]->str_value);;
   uint dummy_errors;
+  arg= args[0]->val_str(&args[0]->str_value);  
   if (!arg)
   {
     null_value=1;
diff --git a/sql/sql_string.cc b/sql/sql_string.cc
index 1dd7b55d136..61731f3b984 100644
--- a/sql/sql_string.cc
+++ b/sql/sql_string.cc
@@ -328,6 +328,9 @@ bool String::copy(const char *str, uint32 arg_length,
 		  CHARSET_INFO *from_cs, CHARSET_INFO *to_cs, uint *errors)
 {
   uint32 offset;
+  
+  DBUG_ASSERT(str != Ptr);
+  
   if (!needs_conversion(arg_length, from_cs, to_cs, &offset))
   {
     *errors= 0;