The underlying cause for these issues is the insufficient sampling of
the bokeh image. For smaller blur radius there will be very few samples
taken, and with 1-pixel radius it boils down to just 4 samples:
2 on the left border (black), 1 in the center (black) and 1 at the top
border (blue) ...
For now have added the workarounds implemented in the CPU version of
that node, which hide these artifacts. Ultimately would be better to
have mipmap levels for the bokeh image input instead.
Lukas Tönne
13553876ba