This is rather common in Finder. First, are you in the Icon View? If so, I've found that it never remembers arrangement settings. If you're in List View, I've found it remembers the settings for a particular folder, but not overall. Example: Visit folder A and arrange by Name. Now visit folder B and arrange by Size. When you go back to folder A, it's still arranged by Name, not Size. Finder leaves a bit to be desired in this functionality. It also doesn't seem to remember settings that you choose and set as defaults.