The new file is after the storateBytes fix.

diff.diff

diff -u /tmp/old.yul /tmp/new.yul
--- /tmp/old.yul	2021-09-28 13:41:14.873051780 +0200
+++ /tmp/new.yul	2021-09-28 13:39:28.096229030 +0200
@@ -53,8 +53,8 @@
 
         }
 
-        function update_byte_slice_32_shift_0(value, toInsert) -> result {
-            let mask := 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
+        function update_byte_slice_1_shift_0(value, toInsert) -> result {
+            let mask := 255
             toInsert := shift_left_0(toInsert)
             value := and(value, not(mask))
             result := or(value, and(toInsert, mask))
@@ -70,7 +70,7 @@
 
         function update_storage_value_offset_0t_userDefinedValueType$_MyInt8_$2_to_t_userDefinedValueType$_MyInt8_$2(slot, value_0) {
             let convertedValue_0 := convert_t_int8_to_t_int8(value_0)
-            sstore(slot, update_byte_slice_32_shift_0(sload(slot), prepare_store_t_userDefinedValueType$_MyInt8_$2(convertedValue_0)))
+            sstore(slot, update_byte_slice_1_shift_0(sload(slot), prepare_store_t_userDefinedValueType$_MyInt8_$2(convertedValue_0)))
         }
 
         function cleanup_t_uint256(value) -> cleaned {
@@ -104,13 +104,27 @@
             converted := cleanup_t_bytes2(value)
         }
 
+        function shift_left_8(value) -> newValue {
+            newValue :=
+
+            shl(8, value)
+
+        }
+
+        function update_byte_slice_2_shift_1(value, toInsert) -> result {
+            let mask := 16776960
+            toInsert := shift_left_8(toInsert)
+            value := and(value, not(mask))
+            result := or(value, and(toInsert, mask))
+        }
+
         function prepare_store_t_userDefinedValueType$_MyBytes2_$4(value) -> ret {
             ret := value
         }
 
-        function update_storage_value_offset_0t_userDefinedValueType$_MyBytes2_$4_to_t_userDefinedValueType$_MyBytes2_$4(slot, value_0) {
+        function update_storage_value_offset_1t_userDefinedValueType$_MyBytes2_$4_to_t_userDefinedValueType$_MyBytes2_$4(slot, value_0) {
             let convertedValue_0 := convert_t_bytes2_to_t_bytes2(value_0)
-            sstore(slot, update_byte_slice_32_shift_0(sload(slot), prepare_store_t_userDefinedValueType$_MyBytes2_$4(convertedValue_0)))
+            sstore(slot, update_byte_slice_2_shift_1(sload(slot), prepare_store_t_userDefinedValueType$_MyBytes2_$4(convertedValue_0)))
         }
 
         /// @src 0:47:166  "contract C {..."
@@ -131,7 +145,7 @@
             let expr_23 := convert_t_uint16_to_t_bytes2(expr_22)
             /// @src 0:123:163  "MyBytes2.wrap(bytes2(uint16(msg.value)))"
             let expr_24 := convert_t_bytes2_to_t_bytes2(expr_23)
-            update_storage_value_offset_0t_userDefinedValueType$_MyBytes2_$4_to_t_userDefinedValueType$_MyBytes2_$4(0x01, expr_24)
+            update_storage_value_offset_1t_userDefinedValueType$_MyBytes2_$4_to_t_userDefinedValueType$_MyBytes2_$4(0x00, expr_24)
 
         }
         /// @src 0:47:166  "contract C {..."
@@ -209,7 +223,7 @@
             }
 
             function cleanup_from_storage_t_userDefinedValueType$_MyInt8_$2(value) -> cleaned {
-                cleaned := value
+                cleaned := and(value, 0xff)
             }
 
             function extract_from_storage_value_dynamict_userDefinedValueType$_MyInt8_$2(slot_value, offset) -> value {
@@ -256,8 +270,15 @@
 
             }
 
+            function shift_left_240(value) -> newValue {
+                newValue :=
+
+                shl(240, value)
+
+            }
+
             function cleanup_from_storage_t_userDefinedValueType$_MyBytes2_$4(value) -> cleaned {
-                cleaned := value
+                cleaned := shift_left_240(value)
             }
 
             function extract_from_storage_value_dynamict_userDefinedValueType$_MyBytes2_$4(slot_value, offset) -> value {
@@ -273,8 +294,8 @@
             /// @src 0:103:163  "MyBytes2 public b = MyBytes2.wrap(bytes2(uint16(msg.value)))"
             function getter_fun_b_25() -> ret {
 
-                let slot := 1
-                let offset := 0
+                let slot := 0
+                let offset := 1
 
                 ret := read_from_storage_split_dynamic_t_userDefinedValueType$_MyBytes2_$4(slot, offset)
 
@@ -306,7 +327,7 @@
 
         }
 
-        data ".metadata" hex"a3646970667358221220830db95fbd84fb1cc4b735fb6b29aed22e28f47972858f202afb14c55cecfe3f6c6578706572696d656e74616cf564736f6c637827302e382e382d646576656c6f702e323032312e392e32382b636f6d6d69742e65323430383361320066"
+        data ".metadata" hex"a3646970667358221220712910874786da4c91f145be60bbefba50ad86b846cf1dcb03da1d794167b6916c6578706572696d656e74616cf564736f6c63430008080041"
     }
 
 }

Diff finished.  Tue Sep 28 13:41:22 2021