For me, each time I open the item list using the menu: Lists | Item List, I get the same result - my saved column widths.

However, I do see that when I use Ctrl-L I see different column widths. Oddly, they are not the default either, and they stick in their own way. If I adjust them, they are saved, and then each time I press Ctrl-L I see them as I last adjusted them - before closing the window. QuickBooks appears to be savings two views of the window. The window's position and size is consistent, but the columns are saved two ways. I never noticed that before.