Hadn't intended to be home around 9am for the next opening, but I'd left an important file at home and had to run home from work around 8:30. Coincidence, I swear! But as long as I was home... Logged in, went to Negilahn. About 5 minutes to 9, the glittery music starts. This time, I was on the correct level and saw the 'portal' appear -- a trace of twinkly lights, tracing out the shape of the symbol that you touch in the Bahro cave, a partial, doubled-back spiral.
My question this time was: when I appeared back in the cave, could I touch the symbol and bring the floating stone back from Relto? (The way you could return the totem poles from the original four Uru ages.) Answer: no. The symbol on the wall doesn't respond to touch. Nothing to do but fall through again. The floating stone is still there on Relto.