Bone matrix assignment behaviour change in Blender 2.80

Hi, I am trying to port an armature importer add-on from Blender 2.79 to Blender 2.8x.

After the bone is being created the bone matrix is set.

But the assignment of the bone matrix has a different behaviour in Blender 2.82a compared to the older Blender 2.79b.

I created a small script that works for both Blender versions to reproduce this behaviour:

import bpy
from mathutils import *

def new_armature(name: str) -> bpy.types.Object:
    armature = bpy.data.armatures.new(name)
    obj = bpy.data.objects.new(name, armature)
    
    if bpy.app.version[1] >= 80:
        bpy.context.scene.collection.objects.link(obj)
        bpy.context.view_layer.objects.active = obj
    else:
        bpy.context.scene.objects.link(obj)
        bpy.context.scene.objects.active = obj

    return obj    
    
obj = new_armature('human')
armature = obj.data

bpy.ops.object.mode_set(mode='EDIT')

new_bone = armature.edit_bones.new('Bone.000')

new_bone.head = Vector([0, 0, 0])
new_bone.tail = Vector([1, 0, 0])

bone_matrix = Matrix(([0,0,1,0],[0,-1,0,-6],[-1,0,0,6],[0,0,0,1]))
print("bone_matrix:\n", bone_matrix)

new_bone.matrix = bone_matrix
print("new_bone.matrix:\n", new_bone.matrix)

Running that script in Blender 2.79b and Blender 2.82a gives me the following outputs:

[email protected]:~/workspace/blender$ blender2.79b --python test2.py --background
Read prefs: /home/user/.config/blender/2.79/config/userpref.blend
found bundled python: /opt/blender/2.79b/2.79/python
bone_matrix:
 <Matrix 4x4 ( 0.0000,  0.0000, 1.0000,  0.0000)
            ( 0.0000, -1.0000, 0.0000, -6.0000)
            (-1.0000,  0.0000, 0.0000,  6.0000)
            ( 0.0000,  0.0000, 0.0000,  1.0000)>
new_bone.matrix:
 <Matrix 4x4 (0.0000,  0.0000,  1.0000,  0.0000)
            (0.0000, -1.0000,  0.0000, -6.0000)
            (1.0000,  0.0000, -0.0000,  6.0000)
            (0.0000,  0.0000,  0.0000,  1.0000)>

Blender quit
[email protected]:~/workspace/blender$ blender2.82a --python test2.py --background
Blender 2.82 (sub 7) (hash 375c7dc4caf4 built 2020-03-12 05:30:40)
Read prefs: /home/user/.config/blender/2.82/config/userpref.blend
found bundled python: /opt/blender/2.82a/2.82/python
bone_matrix:
 <Matrix 4x4 ( 0.0000,  0.0000, 1.0000,  0.0000)
            ( 0.0000, -1.0000, 0.0000, -6.0000)
            (-1.0000,  0.0000, 0.0000,  6.0000)
            ( 0.0000,  0.0000, 0.0000,  1.0000)>
new_bone.matrix:
 <Matrix 4x4 (-1.0000,  0.0000, 0.0000,  0.0000)
            ( 0.0000, -1.0000, 0.0000, -6.0000)
            ( 0.0000,  0.0000, 1.0000,  6.0000)
            ( 0.0000,  0.0000, 0.0000,  1.0000)>

Blender quit

As you can see, the new_bone.matrix matrix differes between these versions.

Updating the scene also does not change anything.

Can you give me a hint how to get the Blender 2.79b behaviour in Blender 2.82a?

My platform is Linux with Kubuntu 19.10 x64.

Update: It looks like the transform roll is not calculated at all.

Best Regards,
phil535