BUG #17141: SELECT LIMIT WITH TIES FOR UPDATE SKIP LOCKED returns wrong number of rows

The following bug has been logged on the website:

Bug reference:      17141
Logged by:          Emil Iggland
Email address:      emil@iggland.com
PostgreSQL version: 13.3
Operating system:   Windows
Description:

I am trying to create a queue which should assign multiple tasks to a
worker. I use row locking with FOR UPDATE SKIP LOCKED, but the number of
rows returned are inconsistent with what I expect. 

Minimum example:
 
CREATE TABLE queue (task INTEGER); 
INSERT INTO queue (task)
VALUES (180),(280),(380),(480),(580),(180),(280),(380),(480),(580);

BEGIN; 
SELECT * FROM queue
ORDER BY task DESC
FETCH FIRST 1 ROWS WITH TIES
FOR UPDATE SKIP LOCKED;
/* Some work to be done here */
COMMIT;

select version();
PostgreSQL 13.3, compiled by Visual C++ build 1914, 64-bit

Expected result Worker 1: (580), (580), Actual result Worker 1: (580),
(580)
Expected result Worker 2: (480), (480), Actual result Worker 2: (480)