Registration page industry selection menus too dynamic!

On MacOSX, in Safari, the account registration page, the industry and subindustry menus are unstable. I selected marketing, with a sub-industry of graphic design and illustration; when I looked back, my selection had changed and was no longer available (only five options left under marketing.) Switching top-level industry back to the default restored my selection, but it went away again when I opened the second menu. How do you do that?