3551152 - In a query, why tables of the same name but belonging to different owners need aliases when they are fully qualified with their owner names - SAP IQ

Consider the scenario below.
2 users own a table of the same name:

create table user1.tab (col_a  int NULL);
create table user2.tab (col_a  int NULL); 

In this query below, both tables are full qualified with owner.table_name.column_name.

SELECT * FROM user1.tab JOIN user2.tab ON user1.tab.col_a = user2.tab.col_a

This error is fired:

Could not execute statement. More than one table is identified as 'tab'
SQLCODE=-139, ODBC 3 State="42000"

If an alias name for each table is specified, then the query succeeds.

SELECT * FROM user1.tab u1_t JOIN user2.tab u2_t ON u1_t.col_a = u2_t.col_a

Why is an alias name necessary for the tables in this scenario, while the tables are fully qualified with their owner names?

SAP IQ 16.1

"correlation name"; "table alias"; alias , KBA , BC-SYB-IQ , Sybase IQ , Problem