The described behavior doesn't occur when blending two 32 bit Forms.
Would you elaborate on your scenario? How do those lower-depth forms come to be these days?
We use `Pen`, which is a subclass of `BitBlt`. More specifically, we use `Pen>>roundNib:` among others to create a circular brush for painting on a `Form`. This method creates a `Form` with depth `1`. One can then set the color of the brush with `Pen>>color:`, which calls `BitBlt>>fillColor:` which in turn sets its `halftoneForm`. According to the class comment of `BitBlt`, the pixel values of the `halftoneForm` are ANDed with the `sourceForm` pixels before the blending rule is applied.
A workaround for us might be to use Pens with 32 bit sourceForms, if that is possible. I only noticed the different behavior of 32 bit forms while trying to create a code snippet to reproduce the problem, so I haven't tried this workaround yet. Also, I think that the problem still occurs when using alpha values between `1` and `254`, even if those might not be as noticeable.