This is usual for all pool-kind-of-mining where you have immature, unexchanged and confirmed balances. What can happen is following:
1. Immature balance goes down due to block(s) becoming orphan.
2. Unexchanged balance goes down due to worse exchange rate.
If the total balance is lower than balance recorded 5 minutes ago, then of course, profitability for that time period is negative.
Considering facts above, ethereum profitability should be always viewed over longer timespan and not short time spans, because short time spans are very "wild" with high ups and high downs, even negative ones.
My average payrate is 0,1151 BTC/GH/Day and that is half of the payrate displayed on the main page. That means I will probably disable Ethereum. I think I this case the Ethereum is wasting my hashing power.