Bug after removing everything from "Normal Work Week" schedule?
 

I removed everything from "Normal Work Week for Project", and then scheduled hours for the project in "Work Schedule for Project" separately for every week. I'm doing this because the project doesn't have a static weekly schedule, it changes completely from week to week.

Looks like this cannot be done. "Scale To Fit Project" won't scale correctly, and also scaling the project by dragging header bar just "zooms in" to the timeline endlessly no matter where the mouse is dragged. I realize that this (empty "Normal Work Week") is a rare situation, but I think that OmniPlan should at least warn the user that empty "Normal Work Week" will not work correctly.

Better would be to fix the calculations in this case. I'm not sure how you would handle the case where there's not enough hours available in the work schedule (e.g., you have marked 200 hours available but tasks would take 300 hours, so the project would never be complete). Maybe some sort of warning would be necessary.