I also fixed a bug with auto-resizing not re-enabling split mode after disabling it when you scale your window down - will help with testing this if you go too far and can't get back again without a refresh: https://github.com/silverstripe/silverstripe-admin/pull/818
Resolves https://github.com/silverstripe/silverstripe-campaign-admin/issues/87
I also fixed a bug with auto-resizing not re-enabling split mode after disabling it when you scale your window down - will help with testing this if you go too far and can't get back again without a refresh: https://github.com/silverstripe/silverstripe-admin/pull/818