I've changed a site content type and set it to update those that inherit from it. However, when I go to create a custom list form based on a list with one of those content types, SPD gives me the old fields. I've checked the list content type and it has all the changes I made, but I can't seem to make SharePoint Designer see them.
If you're creating the list in SharePoint Designer, you should refresh the Data Source Library after your change (or restart SPD). There's a refresh link at the bottom of the Data Source Library pane.