If you were logged in you would be able to see more operations.
LI-T220.127.116.11889 Firebird 3.0 Alpha 2
b as (
select 0 rc
from rdb$database qa
join rdb$database q1 on q1.rdb$relation_id*0=b.rc*0
join rdb$database q2 on q2.rdb$relation_id*0=b.rc*0
select * from b
Result: "Column does not belong to referenced table." (seems that it is 'b.rc' column that is source of trouble).
Same query in LI-V18.104.22.168744 Firebird 2.5 runs OK and return two rows (0 and 1).
The problem disappears if second join: "join rdb$database q2 on q2.rdb$relation_id*0=b.rc*0" - is commented out.