When I turned on the option in config: onlyShowAccessible: true after the player tries to give the item to an empty place, I don't know it, but this item cannot be recovered, it should be blocked from putting items there.

EnderContainers-2.2.0-bug-3
Spigot: 1.12.2
[ProtocolLib] Enabling ProtocolLib v4.5.1-SNAPSHOT-b445

Hello @radek203! Yes, it's a bug 😅 I will fix it as soon as I can.
Thank you for the feedback!

This bug should be fixed with the referenced commit above.
I've made dragging and clicking forbidden in restricted menus.

Here is a little preview:

Best regards.