Changes in Bone Targeting During Model Import/Export

[kafeijk]

• Blender 3.6
• mmd_tools v2.10.2
• Windows 11

I added an 'upper body2' bone to a model without a sub-standard bone (such as the MIKU model from early MMD). After importing the modified model into Blender and then exporting it, I checked it in PmxEditor. Previously, the 'upper body' bone targeted 'upper body2,' but now it has changed to a relative position.
before:

after:

When importing the model, the head and tail are checked using EditBone, but it's not the EditBone type here.
https://github.com/UuuNyaa/blender_mmd_tools/blob/d148bdbd520a0ddb2ffd0389a0217a297ad107f0/mmd_tools/core/pmx/exporter.py#L407C29-L407C83
I'm not sure if the current situation is due to the code or if the file structure is inherently like this.

[kafeijk]

Additionally, if the target changes, the local axes in MMD will also change accordingly.
before:

after:

[KotoriKoi]

This seems to be the problem? I removed 'not' and it worked normally. isMovable in PE seems to indicate whether the bone can be moved. I don't quite understand what lines 270 and 274 want to do the opposite.