Need to help on retargeting character animation!

Hi! I am trying to retarget sword unequip animation onto my character using
IK retargeter, but I run into an issue.

the original animation :
the mannequin has a weapon_r bone attached to his wrist.
and when the sword is being unequipped, its weapon_r bone’s position also stays on the sheath.

녹화_2022_06_15_11_43_48_307

to my custom character :
so, I have added same bone to my character, and used ik retargeter to transfer animation.
and for some reason, his weapon_r bone keeps on following hand bone!
녹화_2022_06_15_11_42_18_161

is ik retargeting facing some limitation?
or am I missing something?

any help would be really appreciated. thank you for reading!