"Database does not exist" weirdness

Hi folks,

Please excuse the question if I'm missing something stupid, but I seem to be stuck. I've created a postgres database, via an Elixir project setup, and it's showing up via psql's \l command, but I'm seeing "database does not exist" messages.

Transcript of a session showing this follows below.

Anything I should be looking at, here? What am I missing?

Many thanks in advance,
Michael

pi(at)raspi ~ $ sudo -u postgres psql
psql (9.4.10)
Type "help" for help.

postgres=# \l
List of databases
Name | Owner | Encoding | Collate | Ctype | Access privileges
--------------+----------+----------+-------------+-------------+---------------------------
testdb | postgres | UTF8 | en_GB.UTF-8 | en_GB.UTF-8 | =Tc/postgres +
| | | | | postgres=CTc/postgres +
| | | | | testdb=CTc/postgres
postgres | postgres | UTF8 | en_GB.UTF-8 | en_GB.UTF-8 |
template0 | postgres | UTF8 | en_GB.UTF-8 | en_GB.UTF-8 | =c/postgres +
| | | | | postgres=CTc/postgres
template1 | postgres | UTF8 | en_GB.UTF-8 | en_GB.UTF-8 | =c/postgres +
| | | | | postgres=CTc/postgres
(4 rows)

postgres=# \q
pi(at)raspi ~ $ sudo -u postgres psql testdb
psql: FATAL: database "testdb" does not exist
pi(at)raspi ~ $ sudo -u postgres createdb testdb
createdb: database creation failed: ERROR: duplicate key value violates unique constraint "pg_database_datname_index"
DETAIL: Key (datname)=(testdb) already exists.

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