If you look at the options for autosplit, you can see what they did:
Autosplit into Projects:
* Two-hour gaps
* Eight-hour gaps
* 24-hour gaps ... except they called this "One project per day" which isn't true either in terms of description or in terms of the date labels they apply to the projects it creates
This would be such a simple fix, it baffles me why they haven't changed it.
I assume (although I haven't tested it) that "One project per week" is actually "168-hour gaps", not actual Sunday to Saturday groupings.