I have found the cause of my original bug and created a sample project showcasing it. I believe there is an iOS7 bug.
As of iOS7, if you create a UITableView with the Grouped style, but do not have a delegate set on first layout, then you set a delegate and call reloadData, there will be a 35px space at the top that will never go away.
See this project I made showcasing the bug: https://github.com/esilverberg/TableViewDelayedDelegateBug
If line 24 is active,
[self performSelector:@selector(updateDelegate) withObject:nil afterDelay:0.0];
there will be an extra 35 px space at the top. If line 27 is active and 24 is commented out,
self.tableView.delegate = self;
no space at the top. It's like the tableView is caching a result somewhere and not redrawing itself after the delegate is set and reloadData is called.