multiple value list error failed

Hi everybody,

I'm running report designer 3.9.1-GA16122
Datasource : Sample delivered with PRD, table CUSTOMERS.
(I can reproduce the same problem with JDBC-mysql and other tables)

I produce a repport and set a parameter. This parameter is a multiple value list type parameter.
If a select one parameter there no problem, but if I select 2 or more parameters, I have an Interal Error.
org.pentaho.reporting.engine.classic.core.ReportDataFactoryException: Failed at query: SELECT DISTINCT
"CUSTOMERS"."CUSTOMERNAME"
FROM
"CUSTOMERS"
WHERE
"CUSTOMERS"."CUSTOMERNAME" = ${param_customers}
at org.pentaho.reporting.engine.classic.core.modules.misc.datafactory.sql.SimpleSQLReportDataFactory.queryData
...snipp...

ParentException:
java.sql.SQLException: Unexpected token: , in statement [SELECT DISTINCT "CUSTOMERS"."CUSTOMERNAME"
FROM
"CUSTOMERS"
WHERE
"CUSTOMERS"."CUSTOMERNAME" = ?,?]
at org.hsqldb.jdbc.Util.throwError(Unknown Source)

...snipp...

Here the parameter request:
SELECT DISTINCT
"CUSTOMERS"."CUSTOMERNAME"
FROM
"CUSTOMERS"
ORDER BY
"CUSTOMERS"."CUSTOMERNAME" ASC

Here the rapport request:
SELECT DISTINCT
"CUSTOMERS"."CUSTOMERNAME"
FROM
"CUSTOMERS"
WHERE
"CUSTOMERS"."CUSTOMERNAME" = ${param_customers}

For the param_customers:
Value type : STRING
Display Type :Multi Value List
Query: parameter
Value : CUSTOMERNAME
Display Name : CUSTOMERNAME


Any hints ?
Thank you for the time you spend