How do I (horizontally) freeze top rows AND divide/split the window vertically (at the same time)?

I have a large spreadsheet, so in order to better move around in it I want to freeze some top rows AND ALSO divide (split) the window vertically, but LO seems to switch from freeze mode to divide mode and vice-versa, never combining them. I know how to use both and if I only want one of them I can make it work just fine, but I want to use both at the same time! Is this impossible?

Since there’s no documented limitation on the simultaneous use of the two functionalities, would this be a bug (rather then an enhancement request, which it isn’t)?