Hello Mike,
The auto roll length function is working almost perfectly for me when I specify both dimensions (custom -> enter specific size). The only problem is it returns a page size slightly longer than needed. If I turn the function off and select "set paper length" it shaves about a centimeter of excess.
This is by design. The auto roll length leaves about 1/4 inch slack on the top/bottom because with many roll printers it is not a good idea to have no leading/trailing space, particularly when using a cutter. If you use something like the "trim" option separately, that goes for the minimums. Auto roll length is also designed so that when you turn auto roll length off and go back to page based placement, the auto arrangement of prints stays the same (prints are not moved to a second page for example).
When trying to use a custom size specifying only one dimension it fails almost every time and behaves erratically. When trying to place an image larger than the actual length sometimes it crops the image (with crop set to off), sometimes it shrinks the image to fit the paper. When placing multiple images sometimes it overstretches the paper leaving half of the page empty.
Printers tested: Canon Pro 4000 (regular driver and XPS), Canon IPF 8400
Windows 10 pro
I am out of the office now, but tomorrow I can send some screenshots and additional info if necessary.
Thanks again for this new feature, I am sure you will get it working 100% soon.
With the current version, you do have to be careful with custom sizing options. The feature was designed to work best with specific sizes and with so many custom sizing options available, you can get yourself into situations that don't make sense. You could, for example, size by one dimension by picking the long side, and the short side could be too big to fit on the width. Since the paper width is set and not modifiable, you've created a situation where the print (as specified) cannot fit on the page no matter how long you make the media length. The print then must be sized to dimensions that will end up fitting the width and that, in turn, will affect what happens when you turn crop off/on. So essentially you've picked "long side" sizing but since the print won't fit, the software had to size by the short side instead.
There are other examples where certain specialized sizing functions may conflict with automatically picking a roll length and we are working through those in future versions. For now, it's best to just specify print size to avoid such conflicts.
Regards,
Mike