As the chest in cash runs is not an account on the site, your Assets do not increase when you are the new owner or last buyer of a cash run.

Your Assets are the sum of your cash and the purchase price of your currently owned pets.

When you are the last buyer your Assets decrease due to a loss of cash. As the last buyer the sum of the purchase prices of your currently owned pets does not increase as the cash chest is not an account on the site. This is a difference between participating in a cash run and a tradition pet run.

Cash runs only affects your Cash amount. Any change reflected in your Assets is due to an increase or loss of cash.