SessionForm: multiple input field issue

Hi :)
I use the nice SessionForm extension from Andreas Schempp for multiple pages submission form.

My problem is: when creating multiple input field like checkboxes or lists, the data don't seem to be retrieved in the 2nd page: when I get the email after final submission, the field shows: "array"...

This doesn't appear when the multiple choice field is set up on the last page of the form: I guess that's because the data doesn't need to be stored in session.

For checking this, I set the first form page to send an email with the datas and everythng is fine: I get all the fields normally... But on the second mail which gather all the data from page 1 and 2, the multiple input fields show "array"...

This is not a big issue, but I would like to be able to get only 1 mail with all the informations ;)
Anyone has an idea about it?
Regards

edit: forgot to mention that I use the 2.7.5 version
Eric