"Mirror" bone setting in posing mode doesn't actually work like a mirror

[RiceBaker100]

Current behavior: When a bone is set to Mirror, moving or rotating it to the left moves the opposing bone to the right and vice versa. This is correct behavior. However, moving or rotating it up moves the opposing bone down and vice versa. Moving it or rotating it forward moves the opposing bone back and vice versa.

Expected behavior: In 3D modeling software, "mirror" means to just flip one axis (in the case of blender, it's the X axis). That way the two halves stay symmetrical no matter what.

What I think is happening: In brio, it seems like the bone with the Mirror setting simply tells its opposing bone to do the opposite movement, essentially flipping all axes, which isn't correct. Instead, only the X axis should be flipped. I can't actually think of a single scenario where the current mirror behavior is desirable.