Banner copying recipe ignores existence of other items in crafting grid

The bug

When copying a banner through the crafting grid, any additional items inside the crafting grid will be ignored. If the craft is to be completed, items will be deleted.

How to reproduce

1. Give yourself a blank white banner:

   /give @s white_banner

2. Give yourself a white banner with a pattern:

   /give @s white_banner{BlockEntityTag:{Patterns:[{Pattern:ss,Color:15}]}}

3. Open a crafting table and place both banners, plus one or more non-banner items, into the crafting slots
4. Collect the copied banner from the crafting output slot
   → Some or all of the non-banner items are consumed

More specifically, one item is consumed from each stack per banner copied.