Yikes. I wanted to add 3 nulls to the Tiger's skeleton so I could animate his nostrils when he sniffs his stripe. When I assigned the nostrils' points to the added deformer nulls the points shot off into the distance.
A search on the xsi discussion group on softimage.com confirmed the issue was related to the reference pose and it having been transformed. There are a few different workarounds listed in the postings. Here is a new variation that worked for me.
1. From the Weight Editor ppg, save the envelope
2. Select the points you want to assign to the new deformer and assign them to any OTHER deformer
3. Select the Envelope Operator and Freeze
4. Select the envelope geometry and set envelope
5. Load the saved preset.