Hi! Thank you so much for reaching out and for your detailed explanation!
You’re absolutely right! It was an oversight on my part not to check that, and I apologize for any inconvenience this has caused you.
I’ve just released an update for the plugin, version 1.1.1, which should fix the issue and also adds the option to choose whether you want items with less than maximum durability to be sellable in the shop.
Give it a try and let me know if it works for you! Best regards!