The banner copying recipes in the crafting grid isn't fully shapeless, causing some scenario where you have to move the blank banner ahead (or in this case, to the left) of the original one.
Steps to Reproduce
Get some banners.
Make a custom banner with dyes in the loom.
Try copy it with the matching colors in the crafting grid, regardless of the positions.
Expected Result
You can copy it, regardless of the positions of the banners inside the grid.
Observed Result
In some cases, you can't copy the banners in some positions where the blank banner is put behind the original one.
Original Description
Banners that have patterns cannot be copied with a white banner.
I'm unable to reproduce this issue, however, was the original banner crafted before you updated to today's preview?