Invisible chair or me lagging 50x ina row.

[COLOR="Indigo"]It's not lag, per se.

I personally have never figured out how they do it, but you CAN set up your character to sit down when nothing is there to be sat on.

~Lyssa[/COLOR]

It could have been due to someone opening up a summoning bag, and having the monsters do touch damage to the person sitting on a bench to push them around.

You can see an example of this on the map bottom East of Henesys. There is a bench-like object you can sit on, which happens to have monsters that move around there.