Even though the manual states that with DETREND= PRICES the prices are "corrected by the average price slope", it does look like "end-point flattening" is actually used (plotting corrected prices shows that).
Would be great to be able to detrend by a linear regression.
I do not want detrending to depend on a single (ending) data point. I want to have an option to detrend based on an linear regression line - which seems a more robust approach.