BlendEffect with mask broken on Imaging SDK 3?

Question

i'm migrating an app from WP 8.1 to UWP ,so i'm moving to Lumia sdk 3 . This effect was working fine in SDK 2

BlendEffect(background, foreground, mask , BlendFunction.Normal , 1f)

but in SDK 3 , the output is only background.

i've tried this

BlendEffect(background, foreground, BlendFunction.Add) the output is ok

So is the mask broken in sdk 3 ? or the format changed ?

my mask provider is StorageFileImageSource the image is 32bit BGRA

Answer 1

24bit BGR works nothing documented