If you create a new layer from a selection, then put a definition query on it, then calculate a field, it will change all of the features in the selection layer, even the features hidden by the definition query.
This is not how the calculate field / definition-query combo works on the original feature class. Just on the selection layer.
What a really cool feature!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
I love esri. Seriously. I love this program. It's great. It works perfectly.