More Time Zone fun

I'm making (slow) progress in my timezone system, and I just noticed
this little behavioral nugget, which surely is a bug. In the system view
pg_timezone_names is a few timezones that use leap seconds. An example
which I tested is Asia/Riyadh87. When I attempt to SET TIME ZONE using
this timezone, I get this:

ERROR: time zone "Asia/Riyadh87" appears to use leap seconds DETAIL:
PostgreSQL does not support leap seconds.

Surely it's a bug to have timezones in the list that result in errors
being thrown? Also, is there a reason that PostgreSQL does not support
leap seconds?
Regards,
- Naz