I found a shading bug while writing some code to dump all shadings in a PDF. I don't know if this affects PDF rendering within PageDrawer or not.
RadialShadingContext and AxialShadingContext use the following code in their constructors to calculate the number of steps (pixels) in the shading and build a lookup table for each step:
The variable "factor" is the number of steps and "matrix" is the parent stream's matrix + the pattern matrix, so this code is taking the current scale and assuming that that is equal to the number of pixels. This works when a pattern is painted onto a 0...1 scaled surface, but otherwise it produces incorrect results.
There's no way to calculate the number of pixels in the device from its scale, or its matrix. Paint#createContext() provides the device bounds Rectangle, which is what we should be using. Indeed, this is handled correctly in the other shading contexts.