Arrows to refs after animated reassignments don't display

[dwhatley19]

Step 3 of
https://web.mit.edu/dwhatley/www/snapdown/web/production.html#s%20-%3E%20%22ab%22%0At%20-%3E%20%22a%22%0A---%0As%20-%3E%20%22AB%22%0A---%0Alist1%20-%3E%20(ArrayList%200%20-%3E%20s%2C%201%20-%3E%20t)%0Alist2%20-%3E%20list1