Title says it all.

Once I've customized my UI in Opera Email for windows (I've hidden the Labels and MailingLists sections of the UI) I'm left with only the email folders tree on the left side of the screen. This is how I'd like it to stay.

However, when I click on some (but not all) of my email folders the Labels section of the UI re-appears below my email folders section.

If I click Hide Labels it goes away, only to reappear if I select those same certain email folders. How do I prevent this? If I hide a UI aspect, I would expect it to stay hidden until I un-hide it.

Sorry to be pedantic here, but are you both talking about Opera (the browser) or Operas Email? Opera Email is what the question is about. Opera Email has neither a Customize menu when you right-click a column nor can you drag the columns to re-order them.

either in the UI or by editing a text file?

Even if it has to be done by editing prefs files, can it be done? I'd like to switch the order of the FROM and Subject columns for all mail folders.