bone streching..

Hello

i have a character that works ok , the problem is when it simulate physic , for example like the image that i attach the foots are snap to the ground the upper part is simulate physic and animation jump , when the animation begin the bone stretch , if i off ragdoll physic all is fine

is there a way to fix this stretching ?
104127-legsquashandstretch.gif

Im no UE4 animation expert, but it looks like the child bone (the foot) is having the same scaling applied to its parent (The shin bone) in the Z axis, maybe there is a way to apply the same scale inverted to the foot?

Or maybe you have the rig set up wrong but I dont know about that