Targeted task:
A blank shield, that is enchanted with Mending and/or Unbreaking shall be decorated with an Illager Banner.
To that end the shield and the banner get put in the 2x2 or 3x3 crafting grid.
Observed behaviour:
The resulting shield doesn't have any enchants anymore.
Expected behaviour:
The resulting shield should be decorated AND have the original enchantments, just like in Java:
Additionally, adding a "standard" banner to a shield in Bedrock works exactly as expected, with it retaining the enchantments when combining them in the crafting grid.
I also had this issue in the most recent version, 1.21.90. I had a shield enchanted with Mending and Unbreaking III and combined it with an illager banner in my 2x2 crafter. Instead of retaining its enchantments and also being decorated with the banner, the shield was decorated with the banner but the enchantments were removed.