EDIT: the median price used for the conversion rate is taken from the price feeds of the witnesses not from the internal market.

To my understanding, this is true when the debt ratio is <10%. As soon as 10% is reached, the conversion rate is calculated based on the STEEM and SBD supply.

It's odd that Steemworld is still showing a debt ratio of 10%.

The point of this implementation is that the debt ration cannot exceed 10%, because as soon as the SBD supply increases or the STEEM price decreases, this ratio is adjusted by the chain to 10%. So I think Steemworld is actually correct. What you can calculate though (and I guess you did that since you mention 12%?) is what the debt ratio would be, if we'd still use the witness feed logic for the conversion rate instead.