BUG #17445: "ON CONFLICT" has different behaviors when its param is passed with prepared stmt or hard coded

The following bug has been logged on the website:

Bug reference: 17445
Logged by: Yaser Amiri
Email address: yaser(dot)amiri95(at)gmail(dot)com
PostgreSQL version: 14.2
Operating system: openSUSE Leap 15.3 / Kernel: 5.3.18-150300.59.49-d
Description:

Hi,
I think I found a bug or at least a confusing behavior that I can't find any
documentation about.

Summary:
I have an INSERT query that has an "ON CONFLICT" and a "WHERE" clause which
suppose to hit a partial multicolumn unique index.
When I try to insert some records in a transaction (one insert per record)
When I pass the parameter which is used in the "WHERE" condition in prepared
statement params, the transaction fails, but if I hard code it, everything
will be OK (no rollback or errors).
Error: `ERROR: there is no unique or exclusion constraint matching the ON
CONFLICT specification`

Here's another weird thing, in the situation in which transaction fails, If
I reduce the inserts to less than 6, it doesn't fail! (It fails on 6th
execution)

How to reproduce:
I tested this on postgres:14.2 docker image and a couple of other versions.
(This is my first report and I'm doing this with the submit form of the
website. I don't know if it escapes characters or not, so I just write some
raw things, sorry!)

I start Postgres:
docker run --rm -p 5432:5432 --name pg -e 'POSGRES_USER=postgres' -e
'POSTGRES_DB=postgres' -e 'POSTGRES_PASSWORD=postgres' -d postgres:14.2

This is the schema file (which contains a table named balance and a partial
index and some configs)
https://paste.opensuse.org/19058183

I import it:
cat schema.sql | docker exec -i pg psql -U postgres -d postgres

This is the query that is OK, It commits successfully and we'll have one
record in the table, I run it:
https://paste.opensuse.org/61559625
cat works.sql | docker exec -i pg psql -U postgres -d postgres
Note: In line 8 you can see I don't pass '2025-01-01' as prepared statement
parameter.

And I make it a parameter and it fails:
https://paste.opensuse.org/44857745
ERROR: there is no unique or exclusion constraint matching the ON CONFLICT
specification
If you delete one of the executions (one of the lines between 14 and 19) and
reduce them to 5 calls, It won't raise an error and works as it should!

Extra info:
Docker Image Name: postgres:14.2
Host Kernel: Linux 5.3.18-150300.59.49-default

Let me know if you need anything else.
Thank you.