Sometimes I read topics where is problem, then some other users throw ideas with possible solutions and at the end user replies: yes, i solved it. Could you be so kind to publish your solution, it would be useful in future for all of us.
Thank you so much Lionel! This is the thread: http://www.seblod.com/community/forums/fields-plug-ins/bug-saving-multiple-select-fields-broken-w-custom-storage