Windows 7 java vers 7 update 51
An enderpearl normally points towards a stronghold. creating a new world in creative mode, then throwing an enderpearl will lead you directly to an end portal, and when you are directly above an end portal, the pearl will float down into the ground, indicating no more horizontal movement is required.
However, it is possible to cause the enderpearls to NOT indicate the position of an end portal if you were to:
1) create a new world
2) move to a far away place such as 1000,75,1000
3) change world spawn with /setworldspawn
4) attempt to locate stronghold with enderpearl
5) dig down
6) no stronghold
NOTE: the enderpearl will point you toward where the end portal would have been if the world was shifted to match the setspawn change, for instance, if you were to set the world spawn back to its original place, the enderpearl's behavior would be rectified, but if you were to move the spawn point ten blocks in the positive x direction, you would also need to expect the end portal to be ten blocks in the positive x direction away from where the enderpearl now indicates.