So, having the chest bone of your Avatar not directly above your spine / having a bit of an angle to it, will result in to the chest looking really weird. It will be moved directly above the spine and will be rotated to 0 0 0.
This is causing a bit of trouble for me and for everyone that uses a Rexouium Avatar, they all have a bit of a rotated chest / spine. I hope you can implement a fix for this.
I also included a few screenshots from the old IK and the new IK.