Issues with auto cell width not working unless you resize the browser window whereby it resizes correctly when using the SCALE HOURS mode.
Just take the scalehours.html demo page and add dp.cellWidthSpec = "Auto";
Run the page and you will see that you still have the extra days missing from the left but no scroll bar. As soon as you resize the page all the cells are resized and you get all 7 days squashed into the containing div area. It doesnt matter if the containing div has a pixel or relative (%) width.
Incidentally and to make thing more complicated! If you select dp.cellWidthSpec = "Auto", have a visible child resource and DO NOT set a rowHeaderWidth value it fills the containing div correctly.
If you set a rowHeaderWidth OR do not have any child resources OR have hidden child resources you get the same faulty behaviour whereby the cell width is not calculated till the window is resized.