I just tested that scenario on a couple of folders here, and the settings stick.
I tried any custom width, then tried the "snap to" width - they all were the same when reopening.
I even tried mounting a volume with a long name, while the window was closed. When opened, it didn't resize it, but instead did the normal file name truncation.
Do other settings stick, such as the view, or column list widths?
It might be returning to a default view - try it with "Always open in icon view." checked. (Show View Options: cmd-J, or right click on folder, or use the settings tool in tool bar)