That's the first thing I checked too. Other properties of warp objects I just found and considered interesting are:
-Unlike typical warps they aren't ignored when nowall is on.
-In SP they actually spawn exactly at (30, -67) from the top-left corner of the warp event, then travel down until they reach a masked pixel, in case of which they stop. Their warping area is a rectangle, starting at approximately (-64, 24) and ending at approximately (0, 80), both relatively to the point the object stopped at.
-A loop made of a warp object and a corresponding warp target on the same tile is inescapable. jjk causes a life loss but the death animation doesn't get a chance to be played and therefore you don't die. And as mentioned before, jjnowall won't work. Although obviously, the game over screen will show up if you lose all your lives.