9.5: tsvector problem

I have never seen this problem before. It occurred while trying to import
a dump (done by 9.5 client of a 9.4 database) also.

Table definition:

-
CREATE TABLE source.annual
(
filename text,
gzipfile text,
id serial NOT NULL,
tsv tsvector,
ut character varying(19),
xml xml,
processed boolean,
CONSTRAINT annual_pkey PRIMARY KEY (id)
)
WITH (
OIDS=FALSE
);
CREATE INDEX xml_tsv_idx
ON source.annual
USING gin
(tsv);

CREATE TRIGGER tsvectorupdate_source_xml
BEFORE INSERT OR UPDATE
ON source.annual
FOR EACH ROW
EXECUTE PROCEDURE source.update_xml_tsv();

And the trigger function:

CREATE OR REPLACE FUNCTION source.update_xml_tsv()
RETURNS trigger AS
$BODY$

begin

new.tsv := to_tsvector('english', coalesce(new.xml,''));

return new;

end
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;

When I try to insert a value into this table, I get:
==================================
ERROR: function to_tsvector(unknown, xml) does not exist
LINE 1: SELECT to_tsvector('english', coalesce(new.xml))
^
HINT: No function matches the given name and argument types. You might
need to add explicit type casts.
QUERY: SELECT to_tsvector('english', coalesce(new.xml))
CONTEXT: PL/pgSQL function source.update_xml_tsv() line 5 at assignment

********** Error **********

ERROR: function to_tsvector(unknown, xml) does not exist
SQL state: 42883
Hint: No function matches the given name and argument types. You might need
to add explicit type casts.
Context: PL/pgSQL function source.update_xml_tsv() line 5 at assignment
=============================================

But I can do

select to_tsvector('English', 'This is a problem')

without a problem.

What is causing this?

Regards
Johann

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