Adding a .jar into addons folder not working anymore?

I presently using the .jar of a binding on the stable release of OH2 (2.0). Dropping that .jar into the addons folder works!
Due to a NPE report of .jar, which was installed via the Eclips Marketplace (hence on OH2(2.1)) I made a test on that version with the .jar being dropped into the addons folder and made sure that this bundle is started. The binding gets displayed in the Bindings section. When trying to add a thing of that Binding, the inbox shows this title (“Inbox > Tankerkoenig Binding > Choose Thing”) only.

When installing the binding via PaperUI it works as expected!

Am I doing something wrong?