While in VMR on three different days I've teleported to a lower block in the nether. I didn't fall any of the three times because there was no way possible for me to fall to those locations, nor did I get hurt. Just a little scary as there are vast quantities of lava in the nether and I would rather not teleport there and die. I have no idea if you can recreate this, but it's happening nonetheless. Also just read a thread about weird teleporting from lilypads, so something seems to be amiss.
Next time it happens, please respond and give us an exact time of the occurrence. This will help me track you down in the logs and see what happened.
@andrewkm It just happened again in the end, about server time 13:10 and some seconds, with TheMightyStag
Also if it helps any, the nether glitch happened once when on a fence post in the fortress and once was when I was going to jump down 2-3 blocks. Both times landed several blocks below with no way of actually naturally falling there.