[FSX] Night & blend troubles

I used blend, waterland and tiff by 3 files without problem. Water is transparent, nice rendering.When i want to create night variation, i have trouble with same files plus one.It seems that the blend mask wasn't used anymore by resample.exe.I tried black or white portion in my night tiff, but same result with the blend mask : land where i have no photoscenery texture is now white and i have no more sea. I tried too the 2 bgl way, one for day only and the other for night, same panic, even if different, for the mask !Bug or advice needed ?thanks a lot.