We call it the double teleport. We have known it as a "glitch" but that' sit. We need to look into that more.
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I mentioned this in another reply too, i think its weird the portals can glitch like that, maybe it gets unintentionally triggered sometimes? Maybe you can find out if they are conditions to be met, and trigger it at will. If you can, then im sure this is intentional and might be a clue.