For a parent class:
and simple Child1 & Child2 entities.
With another entity (let's call it ExternalEntity) having a bidirectional OneToOne relation owned by Child1:
Enough for the context.
removes the ExternalEntity row and the Child1 row. But a dangling row in the Base table is still there for the now inexistent Child1 instance.
Though, a manual delete of either the associated Child1 OR Base row and then the ExternalEntity works.
The problem with the cascading deletion of the parent seems to be only present when deleting through a MYSQL cascading delete from another row which has a foreign key on a child. (Not tested with a foreign key on the parent though)