I've noticed too that Portrait targets require less pages than Landscape and that the software always defaults to Landscape for some time.
Bug? I guess so, it certainly isn't ideal behavior. But then i1P's tendency to not be sticky is pretty legendary and annoying. For example, you pick a target for a profile, build it then quit the software or move to another workflow. Go back to the profile workflow and does that target stick? No, the software picks some silly default you've never used. We see this behavior all over the application. It's clear the people who wrote this package have little experience actually using it. Nothing new here.