Why are elbows/knees of my characters positioned strangely

When retargeting motions from one character to another, it may happen that the elbows/knees are inversed relatively to their original position (see below).

NB: these options do not apply when replaying a motion made on a character and played on the same character. In this case, it will be played perfectly in all cases

In this case, checking the "IK Plane roll from animation" on the Motion Behavior playing the motion can fix the problem.

However, as in the above image, sometime the morphology of the motion source character and destination character are too different and you would like the elbows or knees to be spread more widely.

It is possible to adjust this by using the additional IK offset options in your Motion Mapping File.