When the Price of STEEM/SBD Falls, Payout Goes Down, When STEEM/SBD Risesm, Payout Does Not Go Back Up???

I just checked the dates of my posts and checked the price of STEEM and SBD at the time. They were roughly the same as they are now, but because STEEM and SBD dropped in price yesterday, the payout's for my posts are almost halved.

Is this normal behavior? Or am I missing something?