Hey David,
just got an information from the MultiWoo developers. Here are there comments.
“MutliWoo does not change session variables directly, it changes only the cart that is saved in the session. It seems that Multiwoo and the theme are using both the same hook and the functions of the theme is called first. You would need to change the priority, that the multiwoo funtion is called first and then the theme function.
the hook is:
woocommerce_check_cart_items
If theme request gets a lower priority the problem should be sloved.”
Is that possible?
cheers.
J