installation - Installed PostGIS extension not listed for database?

I have a PostgreSQL database with the PostGIS extension enabled.

I know that this extension is enabled, since I am using PostGIS functions, and I can actually see the PostGIS functions.

However, PostGIS is not listed in the installed extensions section, and thus I can't alter it nor uninstall it.

If I try

CREATE EXTENSION postgis;

it tells me that PostGIS is already installed, and that I should uninstall it first. However

DROP EXTENSION postgis CASCADE;

tells me that no PostGIS extension is installed.

What can I do? Any ideas?