BUG #17502: View based on window functions returns wrong results when queried

The following bug has been logged on the website:

Bug reference:      17502
Logged by:          Daniel Farkaš
Email address:      daniel.farkas@datoris.com
PostgreSQL version: 10.10
Operating system:   Linux
Description:        

Hey,

Please be gentle, I've never been in contact with Postgres developers.
In short, I've created a view, which has rather sketchy window functions,
but it gives me results I need.
When I do select * on it, it gives me what I expect. One of the columns has
five distinct values.
But when I do group by on that column, it gives me only one of the values.
When I drop the view and create materialized view, all is good, I get all
five values.

My guess is that some parts of the inner select are affecting outer, view's
select, which is not something I would expect.
My current Postgres is PostgreSQL 10.10 on x86_64-pc-linux-musl, compiled by
gcc (Alpine 8.3.0) 8.3.0, 64-bit.
If you think this is worth investigating further, I will try composing a
simpler example, and test it in a more recent Postgres version.
Maybe it's a known limitation I'm not aware of.

Let me know what you think.

Daniel