rookie question

This is an old question which I should asked a long time ago,my character has no twist joint, so I left the twist joint blanked on retarget panel,but the result shows the upperarm of model has collapsed, just like the vertices have weighted to another joint, the thing is Neither of my two characters have weighted to any twist joint, I tried to modify retarget panel, changed the twist joint target to some joint exist like upperarm lowerarm etc, but it didn’t go well. Anyone has the same experience?They always occured in the middle of the upperarm-lowerarm and lowerarm-hand joint.