Untradable Evo Ring II and Tradable Evo Ring II stack.

Some people are saying on Sleepywood that untradable and tradable rings could stack from the first event, so it's possible this isn't a glitch and it won't be fixed.

That's not true actually. My guildmaster has a level 16 untradable Evo Ring 1 and cannot wear it with the level 17 tradable Evo Ring 1 in his possession. We'll have to wait and see how Nexon handles this (if they even bother).