public void test() {
        
        ResetBasicData.reset();
        
        List<Object> idList1 = new ArrayList<Object>();
        idList1.add(1);
        
        String oq = "find customer where id in (:idList)";
        Ebean.createQuery(Customer.class, oq)
            .setParameter("idList", idList1)
            .findList();
        
        List<Object> idList2 = new ArrayList<Object>();
        idList2.add(1);
        idList2.add(2);
        
        Ebean.createQuery(Customer.class, oq)
            .setParameter("idList", idList2)
            .findList();
    
        
    }

Fixed in HEAD.

The fix involves taking the size of the collection (and the property name etc) into account when calculating the query plan hash.