Subsurface scattering changes between path / bidir engines

[universalsd]

I have created a demo scene where the SSS changes drastically just by switching from bidirectional to path tracing. I have tried various scales for the object and it was all the same. Obviously the path traced one looks correct. What am I doing wrong with bidirectional? I have attached my scene

Edit:This is the correct comparison, with bidirectional on the left and path tracing on the right

[Sharlybg]

From my POV it is a normal behaviour. Bidir is a more advanced engine capable to bring more light data to the final image compared to simple path. It is obvious for complicated simulation.

[universalsd]

unfortunately i had an error in my post, in the first image the labels are reversed. Here is how they correctly are. You can see a problem with bidirectional across the board. Subsurface scattering has a "darkening" effect

[Dade]

I may know where the problem is, I'm checking.

[Dade]

Blender Suzanne is an "open" object (there are holes and overlaps) so it can really mess volume computations. I replace the Suzanne with a cube a done some test.

This is path:

This is BiDir:

The light tracing contribution in hybrid rendering (something plain path tracing doesn't render at all) is very significative:

so I'm not sure if you are just observing a normal difference in what path tracing can not render or there is a real problem (aside from the Blender Suzanne problem).