I am clicking on deformation module in network, then clicking copy resting position to current, though when I click out of the setup mode the deformations change and warp my drawing. Can anyone give me a hint what I might be doing wrong please?
Just in case you do not realize it, are you clicking on the Deformation Group or a single Deformation module? You should select the Deformation Group module that would be present if the group were not expanded to show its content. IOW, the Group parent in the Timeline.
When you are not in Setup Mode and you manipulate a green Bone, select the Deformation Group, then click Copy Resting Position to Current the original resting position is copied to the current frame. The resulting pose will be influenced by the previous keyframe pose (if there was one), your most recent pose and the current resting position.
When you are in Setup Mode and you manipulate a red Bone, select the Deformation Group, then click Copy Resting Position to Current the current red bone becomes part of the resting position. When you turn Setup Mode off the red and green bones should be lined up.
At least this is the way it seems to work to me. When I tested and retested this again it followed these rules but there may be other things that my tests are not exposing. This is what I see from reading and experimenting.