Now, I'm not sure if this is related to an individual parcel or the sim the parcel is on, but let me explain as see if anyone can work out why this happens.
There is a 1024 sized plot on a mainland sim.
On this plot (approx 370 in the air) is a skyhome, sitting on some normal 8x8 prims (to make a base) All pretty normal stuff.
The owner of the parcel has no security, nothing odd set on the land.
He can stand on his land, made a TP location and TP onto his "sky" land fine, as you would expect.
But for others, this does not work.
they stand on the land, make a TP landmark and try to use it.
they end up on the ground beneath the land, at the correct x,y position, but at mainland land height.
sometimes (very occasinally) using the same teleport a second time, might take them up to the correct Z position but this is rare.
Yet, on a neighbouring sim there is another sky platform at almost the same height, and Teleport landmarks work fine to that every time, as indeed they normally always do.
It was so much of a pain as to get around it, we have set up a teleporter on the ground to take you from ground level up to the sky plaftorm as normal teleport/landmarks fail all the time.
And ideas why this might be, or what could be done to make it work?
Why would a landmark/teleport not remember it's height in one location?