PostgreSQL / MariaDB, isolation differences

The following sequences of SQL statements are executed on two different connections to the same database.

1: START TRANSACTION ISOLATION LEVEL SERIALIZABLE;
1: UPDATE Person SET LastLogin=NOW() WHERE IDPerson=1
[...paused...]

2: START TRANSACTION ISOLATION LEVEL SERIALIZABLE;
2: INSERT INTO Log (FKIDPerson, Hash) VALUES (1, '95baa69a26a95db2');
2: COMMIT

[...continued...]
1: COMMIT

Column Log.FKIDPerson references the primary key Person.IDPerson (ON UPDATE NO ACTION ON DELETE CASCADE). This runs in PostgreSQL without trouble. I am trying to port it to MariaDB for a customer (only difference in this minimum example is a slight syntax change in opening the transaction), but the INSERT statement of the second connection runs into a lock.

I need exactly this sequence of statements and - for reasons beyond the scope of this small example - I need them nested. How can I instruct MariaDB that this is not a problem (changing the isolation level all the way down to READ UNCOMMITED does not help)?

Update:

While moving LastLogin into a separate table does fix the current problem it cures the symptom not the cause; Log must be writable in separate transactions; I might end up in future versions with moving many or all attributes of Person to a separate table.

How about breaking up the referential integrity here (only in the MySQL version) and replacing it with a trigger on Person deleting obsolete Log records? It feels horrible to me, but after all the only real risk are some stale records which - in case - could easily be found and cleaned. Any opinions?