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 LOCATIOSubject: [BUGS] BUG #4567: Clustering on
GISTINDEX clobbers records in table Subject: [BUGS] BUG #4568: sporadic error doing COUNT(*) on empty tableSubject:
[BUGS]BUG #4572: Incorrect error message when using wrong password wSubject: [BUGS] BUG #4573: download problemSubject:
[BUGS]BUG #4574: LIKE fails on non-varying character with no wildcarSubject: [BUGS] BUG #4575: All page cache in
shared_bufferspinned (duplicatedSubject: [BUGS] BUG #4576: Postgres Windows service crashesSubject: [BUGS] BUG #4578:
Notreleaseing memory from PQmakeEmptyPGresult whenSubject: [BUGS] BUG #4579: to_char & utf8Subject: [BUGS] BUG #4580:
selectsubstring ('a' from '(b)?(a)') returns nullSubject: [BUGS] BUG #4581: Difficult uninstallSubject: [BUGS] BUG
#4582:Renaming sequences and default valueSubject: [BUGS] BUG #4583: Db stopSubject: [BUGS] BUG #4584: PostgreSQL
servicedoesn't startSubject: [BUGS] BUG #4585: out parameter name cuases disruption in custom aggrSubject: [BUGS] BUG
#4586:Supporting of Binary instead Bytea for Primary KeysSubject: [BUGS] BUG #4588: post gres installation
problemSubject:[BUGS] BUG #4589: Postgressql database server 8.3 service fails to stSubject: [BUGS] BUG #4591:
postgres.exemore than 150 processes runnedSubject: [BUGS] BUG #4596: information_schema.table_privileges is way too
slowSubject:[BUGS] BUG #4597: Can't join the mailing lists!Subject: [BUGS] BUG #4599: bugfix for contrib/dblink module
 
        regards, tom lane