"AT TIME ZONE" with zone name PostgreSQL bug?
Actually, the documentation says clearly that the time zone name and abbreviation will behave differently.


  In short, this is the difference between abbreviations and full names:
  abbreviations always represent a fixed offset from UTC, whereas most
  of the full names imply a local daylight-savings time rule, and so
  have two possible UTC offsets. Reference


FWIW, that same reference also says


  We do not recommend using the type time with time zone (though it is
  supported by PostgreSQL for legacy applications and for compliance
  with the SQL standard).