Its a combination of two factors, first the person is aware and concious even while reduced to aether so they can definately get around someone or something.

Second return and teleport are spells that are tried and tested over many years and chances are extremely high those spells and the aetherytes have some built in safety measures. there's a couple of sharlayan leves that explain that in the course of experimenting with wood for aethrytes they accidentally lost a member mid teleport and thus the second leve asks for another wood so they can retrieve him.