error on CREATE INDEX when restoring from dump file: could not read block 0

Hi,

I'm getting the following error when restoring my database from a dump file in postgresql 9.4

--------------
psql:tmp/mydb.out:159861: ERREUR:  n'a pas pu lire le bloc 0 du fichier « base/28903/29447 » : a lu seulement 0 octets
sur 8192
CONTEXTE : fonction SQL « dossier_contrat » lors du lancement
--------------

In English : ERROR: could not read block 0 from file « base/28903/29447 » : 0 bytes read out of 8192

"dossier_contrat" is a simple sql function (definition below) used in an index, whose creation always fails when
restoringfrom a dump file (on different machines),  

I can create the index in psql with :

CREATE INDEX tbldossier_id_contrat_idx ON tbldossier USING btree (dossier_contrat(id_dossier));

but subsequent dumps/restores will always fail on it (only in 9.4, it works fine in 9.1).

What should I be looking for to find the cause of the error?


-------------------
Function definition:

\sf+ dossier_contrat
        CREATE OR REPLACE FUNCTION public.dossier_contrat(integer)
         RETURNS integer
         LANGUAGE sql
         IMMUTABLE
1       AS $function$
2       -- renvoie l'id du contrat couvrant un dossier statutaire
3          SELECT t1.id_contrat
4          FROM tblcontrat t1 INNER JOIN ( tblagent t2 INNER JOIN tbldossier t3 using (id_agent) ) ON
t1.id_collectivite= t2.id_collectivite AND t1.id_caisse_retraite = substring(t2.id_affiliation FROM 6 FOR 3) 
5          WHERE t3.date_origine BETWEEN t1.date_debut_garantie AND t1.date_fin_garantie AND t3.id_dossier = $1
6       $function$


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