Yeah man, this is due to my sucky Javascript which I've been wanting to fix for a while (and would happily accept patches for ). Basically, the page is running a few asynchronous HTTP requests at the same time using $.post() in that set_line_item() function. Well, they don't always get returned in the same order you call them, so it results in overwrites. I need to either devise a new way of doing that or add some sort of custom mutex that will ensure things get fired off in order. Any ideas?