Right so the Gantt bar should span over the 4 days in your first example. What i am saying is that when you change the Hours of a day in the Project settings, and have custom work days, the Durations Column updates with the new settings for the project hours per day but the Gantt bar does not.
Did you follow the steps in the first post? Give it a try and let me know what happens. What i am saying is that i think there is a bug that has the duration column linked with the hours per day field in the project settings but the gantt bar does not update if you change the hours per day setting when the assigned human resource has a custom work schedule. Just give the steps in the first post a try.
PS. WBS stands for work breakdown structure. The 1, 1.1, 1.1. etc is called a WBS.
I did try out your example, and it behaves just as I described. There is no need for the gantt bar to update because the work scheduled has not changed. The hours per day setting in the Project: Formatting inspector has nothing whatsoever to do with the actual scheduling of the work, only convenience of display and entry. OmniPlan uses that value to convert "1 day" into however many hours that is according to your setting but that setting does not reflect individual or project work days unless you set it to the proper value (if that is even possible). If you type "1 day" into a effort field before assigning a task to a resource, OP multiplies 1 day by whatever value you have set for project hours per day and inserts that number of hours in the duration field. It can't very well look at the work schedule of a resource that has yet to be assigned, can it? Neither can it necessarily know when in the week the task will fall for those resources with irregular schedules. When you tell OmniPlan a task involves "1 day" of effort, that is 1 standard project day, which may not be the same number of hours as the work day for any individual resource in the project.
Put yet another way -- this all goes away if you uncheck all units except hours in the Durations Display of the Project: Formatting inspector.