Is this a bug ?

We noticed this bug in Redshift. It then occurred to me that this may
very well be a PG bug since Redshift is based on PG.

Reproduced it in Version 11.5

create table bugtest (fld1 char(1)) ;

insert into bugtest values('a');
insert into bugtest values('b');
insert into bugtest values('c');
insert into bugtest values('d');
insert into bugtest values('e');

select count(*) from bugtest where fld1 in ('a','b','c',
'd','e'); -> produces 5 as output.
So far so good.

Now check this:

select count(*) from bugtest where fld1 in ('a','b','c'
'd','e');

Note the missing comma after 'c'.

PG takes it a syntactically right SQL and gives 3 as output.

In SQLServer it errors out SQL Error [102] [S0001]: Incorrect syntax near 'd'.

Can't believe this bug was never found before. We ended up wasting lot of time to figure this out.