Iceberg Alter partition creates NULL partitioning

[PPL-TBSK]

Is our issue related to this issue #26492 ?
Is this other issue?
Or is our issue expected behaviour?
Trino version used - Starburst 474-e1

Steps to reproduce:

create table test 
(
    a int,
    b int
)
with (partitioning = array['truncate(a,10)'])
;

show create table test;

insert into test select 10,0;
insert into test select 20,0;
insert into test select 30,0;
select * from "test$partitions";

returns 3 partitions { a_trunc = 30 }, { a_trunc = 20 }, { a_trunc = 10 }

ALTER TABLE test SET PROPERTIES partitioning = array['truncate(a,20)'];

select * from "test$partitions";

returns 3 partitions { a_trunc = 30, a_trunc = NULL }, { a_trunc = 20, a_trunc = NULL }, { a_trunc = 10, a_trunc = NULL }
Basically same partitions but with a_trunc = NULL being second partition column

set session iceberg.expire_snapshots_min_retention = '0d';
set session iceberg.remove_orphan_files_min_retention = '0d';


alter table test execute optimize (file_size_threshold => '1200MB');
ALTER TABLE test EXECUTE expire_snapshots(retention_threshold => '0d');
ALTER TABLE test EXECUTE remove_orphan_files(retention_threshold => '0d');

select * from "test$partitions";

returns 2 partitions { a_trunc = NULL, a_trunc = 0 }, { a_trunc = NULL, a_trunc = 20 }
with first partition column being a_trunc = NULL. Is this expected behaviour after optimizing the whole table and deleting all the old data files?
Or is this Issue related to our issue? Each time we would change partitioning on a_trunc column more and more a_trunc = NULL partitionings would be created.

Thanks