i had boots on with protection 4 feather falling 4 unbreaking 3 depth strider 3 and mending, i got boots with protection 1 and thorns 1 from villager trading, i right clicked with them in my hotbar and the same enchantments that where on my boots i had on where applied to the boots i got from villager trading.

-the items keep durability

how to reproduce

have enchanted boots on (don't know if it happens to other armor pieces but i would thinks so) then have enchanted boots in your hotbar and right click with them in your hot bar.

this bug occurred playing on a sever with bedrock dedicated server while playing on windows 10 desktop