You end up half a block lower than the destination warp, causing you to fall through the ground and suffocate to death.

This happens even if you /warp /spawn or /home other places after the first /warp, and as far as I can tell the only way to break the cycle / save your items is to warp somewhere more than a block off the ground, which will still kill you with fall damage anyway. Or, hope you die somewhere above the bottom of the world, and do a quick /back to grab your stuff before /home.

My apologies for petition #4033, that was due to this glitch and not the warp in question.