It does that only with a specefic character, or all?
And with a specific pose or all?
Yes I think it's for a physic conflict, but it could be for many different causes.
It can be because the new character is taller or smaller (can be just for one part of the body, exemple just longer legs) and it can have physics problem against an environement collision(the floor, or other). Or it can be the difficulty to match the pose position with the new bones. It can be also that the character has different joint spring/damper values.
By the way, if it does that, you can:
-move a bit the nodes who seem to cause problems, try put the node position and rotation OFF and ON again
-tweak the person control physics values to see if it helps
Control & Physics 2 “Name Space” By default this will say “Person”. This will display the name of the currently selected Person Atom. You can rename it here as well. Please see Person Atom Basics for general information regarding the Person Atom. Setting a joint to “Control” means that the...
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-change the physics value of a specific node
Person Atom Joint Physics Tab ”Select Root” Is a quick shortcut available on all Person Joints to take you to the Person Atom Root Control node. VaM Atoms are made of two significant parts. The Atom Control and The Physics Object. The “Atom Control” (Green Square) is the node that you...
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I hope It will helps you