Warps between different worlds always teleports you to the spawn of the world. If you teleport a second time then, it teleports you to the right location. Is this a bug of bukkit?
I think it'd be a bug in whatever mod you're using to facilitate warping. For instance, with Wormhole X-Treme I'm put at the right spot, but WorldWarp was putting me at 0x0. I think it's up to the mod as to what coordinates you're placed at during transition. Assuming you aren't accused of hacking and disconnected, which has been happening to me a bit lately when going between worlds...
Nope. The "Player.teleport(Location)" function does not work corectly. It's a bug of bukkit... (Also tested it with MyWarp, MyHome and EasyTravel... anyone works, and as I developed EasyTravel, I know how it should work, if bukkit would do it correct.)