Missing bug-report numbers?

There's somebody over in pgsql-bugs complaining about lack of response
to his bug report #4593. Well, no such bug number came by here, nor is
it in the archives. The adjacent bug numbers are also missing, and I
notice quite a few other gaps. What might be the cause of missing
bug numbers?

For reference sake, the last couple dozen bugs that did arrive here are

Subject: [BUGS] BUG #4566: pg_stop_backup() reports incorrect STOP WAL LOCATIO
Subject: [BUGS] BUG #4567: Clustering on GIST INDEX clobbers records in table
Subject: [BUGS] BUG #4568: sporadic error doing COUNT(*) on empty table
Subject: [BUGS] BUG #4572: Incorrect error message when using wrong password w
Subject: [BUGS] BUG #4573: download problem
Subject: [BUGS] BUG #4574: LIKE fails on non-varying character with no wildcar
Subject: [BUGS] BUG #4575: All page cache in shared_buffers pinned (duplicated
Subject: [BUGS] BUG #4576: Postgres Windows service crashes
Subject: [BUGS] BUG #4578: Not releaseing memory from PQmakeEmptyPGresult when
Subject: [BUGS] BUG #4579: to_char & utf8
Subject: [BUGS] BUG #4580: select substring ('a' from '(b)?(a)') returns null
Subject: [BUGS] BUG #4581: Difficult uninstall
Subject: [BUGS] BUG #4582: Renaming sequences and default value
Subject: [BUGS] BUG #4583: Db stop
Subject: [BUGS] BUG #4584: PostgreSQL service doesn't start
Subject: [BUGS] BUG #4585: out parameter name cuases disruption in custom aggr
Subject: [BUGS] BUG #4586: Supporting of Binary instead Bytea for Primary Keys
Subject: [BUGS] BUG #4588: post gres installation problem
Subject: [BUGS] BUG #4589: Postgressql database server 8.3 service fails to st
Subject: [BUGS] BUG #4591: postgres.exe more than 150 processes runned
Subject: [BUGS] BUG #4596: information_schema.table_privileges is way too slow
Subject: [BUGS] BUG #4597: Can't join the mailing lists!
Subject: [BUGS] BUG #4599: bugfix for contrib/dblink module

regards, tom lane