Hi Rick,

There is a mechanism where when the supply of SBD exceeds 10% of the Steem supply then the price feed conversión keeps higher to avoid flooding the market with a lot of STEEM and keep pushing down the price.
I think the price is set by the witnesses (or the variables which is calculat ed).

I think you can learn more about this in some @exyle @penguinpablo and @themarkymark (not sure if i writed it properly) posts

Espero que te haya ayudado amigo.
Saludos.