Update:
I have fullfilled the co-creator request, both items in the list have been updated.
I received an email is if I was the customer, that the customization was done.
Just now, while testing, If I fill out a co-creator without logging in using a different browser.
I added it to the cart, where it does not show a preview, and I cannot visit the link any more:
https://www.shapeways.com/model/208832/ambicage.html
However as soon as I had added it to the cart, it showed up under "my designs" in my other browser, where I am logged in as virtox.
Removing the models from the cart (anonymous), does not remove them from my design. (virtox)
So if someone fills out a co-creator anonymously and adds it to the cart, it shows up in "my design" of the designer.
The status is NOT "available to all", probably explaining why the ordering user can not see the model anymore..
With the designer account I can remove the filled out co-creator model..
Hope this helps in tracking the issue.