With this simple configuration now the main window is always with width 2. It doesn't matter whether I set main-pane-width: 160 or not, it's always loaded in a strip of just 2 columns.

session_name: foo
windows:
- layout: main-vertical
  panes:
  - blank
  - blank

I'm using the package from AUR.

Issue is present both in vertical and horizontal layouts.