I have only seen the issue ever appearing when you click on the altar, so my guess is that there's an issue with the altar somehow, but I can't imagine how it'll cause you to change heights and glitch :O
I know, I can't figure that out either. I wish I could help you out some more, but I have honestly no clue. Haha.
You can try soloing the Bandos boss yourself and do what I did by running towards the altar while going back to attack the boss to delay some attacks, and also turning your screen in order to see the boss.
Or maybe it was a random event? (Mime)?
Not sure if it would help you solve, but I was using the downloadable client, running as OpenGL (suggested), and first clicking on the "Fixed-Screen Mode," then clicking on the "Resizeable-Screen Mode" in the tools graphic settings. I click both of those in that order because it's a perfect size for me. You can try it yourself in order to see the difference in size.
I was also using full Verac which I was borrowing from L range L, woodcutting cape, glory, bandos gloves, spined boots, and ring of wealth or something. (I think.)
It hasn't done it again since then. Another possibility was that it was the maps that was downloading.