my app was running fine under ios6.1. tried the ios7 simulator and the following part does not work:
EditingCell *cell = (EditingCell*) [[textField superview
I was finding cells the same way you were. Now I use this quick method if I have a button in a cell and know the tableview I'm in. It'll return the tableviewcell.
-(UITableViewCell*)GetCellFromTableView:(UITableView*)tableView Sender:(id)sender {
CGPoint pos = [sender convertPoint:CGPointZero toView:tableView];
NSIndexPath *indexPath = [tableView indexPathForRowAtPoint:pos];
return [tableView cellForRowAtIndexPath:indexPath];
}