BitmapForCaching causes blending issues when drawing with GDI

If I create off screen buffer with BitmapForCaching then it will cause blending issues issues when drawing with GDI

So for example if I create Picture with BitmapForCaching , then I fill it with white using Xojo FillRect, then I fill a rect using GDI (100% red), and the result is 50% red.

Is there any way to avoid this blending effect ?

Same thing does not happen if I create the off screen buffer with NewPicture. Then result of the GDI drawing will be 100% red