Multiple `add` commands within one frame don't work

[dwhatley19]

Compare:

https://web.mit.edu/dwhatley/www/snapdown/web/production.html#a%20-%3E%20(ArrayList)%0A---%0Aa%20add%201%20-%3E%20%22b%22%0Aa%20add%202%20-%3E%20%22c%22

https://web.mit.edu/dwhatley/www/snapdown/web/production.html#a%20-%3E%20(ArrayList)%0A---%0Aa%20add%201%20-%3E%20%22b%22%0A---%0Aa%20add%202%20-%3E%20%22c%22