Problem Summary:

before:
```sql
mysql> select/*+SET_VAR(debug_skip_fold_constant=true)*/ cast('2010-01-05 08:15:30Europe/London' as datetime);
+------------------------------------------------------+
| cast('2010-01-05 08:15:30Europe/London' as datetime) |
+------------------------------------------------------+
| 2010-01-05 15:15:30                                  |
+------------------------------------------------------+
1 row in set (0.19 sec)
```

now:
```sql
mysql> select/*+SET_VAR(debug_skip_fold_constant=true)*/ cast('2010-01-05 08:15:30Europe/London' as datetime);
+------------------------------------------------------+
| cast('2010-01-05 08:15:30Europe/London' as datetime) |
+------------------------------------------------------+
| 2010-01-05 16:15:30                                  |
+------------------------------------------------------+
1 row in set (0.12 sec)
```