I have experienced failures in DOE with shape parameters from SpaceClaim because the dimension change caused a face to be consumed which is not recovered when the dimension returns to the original value. That is why I prefer DesignModeler for shape optimization. However, you seem to have checked that this is not the case for your model.
I don't know what you mean by a parameter being demoted. Can you show an example of what that looks like? Can you upload your .wbpz archive file and provide instructions to reproduce the error?