So, I did the FATE at 15, 18 with the Antelopes in South Shroud (Antelope Parting).
As the FATE ended, the Antelopes ran away. I chased after because 1 was very low on HP and I decided to try to Assassinate it to get a wee bit more EXP.
As I did Assassinate, the Antelope faded away, and as I did Assassinate, it turned me Invisible, and locked my model in mid-air, tilted, at 15, 19, as GM Zuhyramm can attest to with this image taken by me and given to GM Zuhyramm:
Click for bigger image.
Furthermore, the sound vanished and I was unable to hear my footsteps. I could however hear the skills going off, and other players. - Tried to recreate the bug (time: 06:09 a.m. 30 minutes before this post was posted) but was unsuccessful in doing so as I failed to do Assassinate in time.
Other players could see me. When I zoomed in on myself, it seemed to tell me that I was underground, which was odd, since I was floating in the air (what I saw), or standing normally on the ground (what others saw). If I tried to target myself, I was directed to where my model was, and when I moved, the model moved and so on.
Thanks to GM Zuhyramm who showed patience.