I took a look at simplifying this test case, and I think it comes down
to data types:
maciek=# select 9/10;
?column?
----------
0
(1 row)
maciek=# select pg_typeof(10);
pg_typeof
-----------
integer
(1 row)
But:
maciek=# select 9/1e1;
?column?
------------------------
0.90000000000000000000
(1 row)
maciek=# select pg_typeof(1e1);
pg_typeof
-----------
numeric
(1 row)
Does that explain the behavior you're seeing?