Runes of Magic US / AU

You get the same affect if you go slow. Click gate once you transport outside castle, click gate again you transport inside castle. So, you are saying that if you click the gate twice you end up back inside? Is that not what is supposed to happen? Your lag just caused you to miss viewing the microsecond you were outside.

Whenever you doubleclick on any other gear point, or even harvest point in the open world, I believe you use it, then immediately stop using it (or possibly restart using it as if you just clicked on it (wait, you did)). This is the same with the gates. You double click on something that teleports you, of course it would teleport you through, then back through, as the game registers two clicks.

Perhaps a small validation timer could be implemented to say "Player12345 clicked on gate 2 times within <5 seconds, invalidate the second click". however I'd wager to imagine that such a mechanism within the game code would lead to even more lag than what is present already in siegewar on some days.

I would call that a suggestion though, not a bug. In this case you doubleclicked on a mechanism to teleport you, so it's only logical that you get teleported through that object twice.