I managed to fix the issue for now, but I'd regard my solution rather a quick and dirty hack than something worthy to be in the OFBiz codebase. Anyway I'll post it here asap.
(As a side note I'd rather see the Anonymous Quick Checkout programmed more the way Quick Checkout is done, i.e. with the amount of client side jQuery wizardry reduced to the max.
I know there has been plenty of discussion on this topic, and sure I'm a big fan of jQuery myself (and glad that ofbiz moved to this toolkit), but those very checkout pages are the place where the fate of any B2C webshop is sealed, so why take any chances here instead of resorting to a maybe less elegant but more robust server side solution.
The original dojo.connect() method itself is deprecated now as are some older jQuery methods that have been replaced by jQuery.on(), so I'd rather avoid keeping up with all those changes in crucial places if possible.
I'm a new member of the great OFBiz community, so if I rehash an old worn-out issue here please disregard this part.)