I'm not sure if this is a bug with the compass or if the game thinks that the spawn point is actually moving. I'm trying to map out my spawn chunks, so I started my crafting a compass and marking my spawn point, found with the compass. I then left a trail of items from the spawn point going 128 blocks away to a Nether portal I had crafted.
When I come back from the Nether to the Overworld I notice two things.

1. That all of the items that were dropped in the 128 bock area are still there. This shouldn't happen if the spawn point is approximately in the center of the spawn chunks, as has been the case in previous versions.
2. My compass pointed to a different location than my original spawn point. I have not been able to find a pattern; sometimes the new spawn point is far away, and sometimes it is in the same chunk as the original.

Something else related to this issue is that when I die or relog, then the compass points to the original spawn point again. Also, If I have not slept in a bed, I respawn back at the original spawn point.
So the new spawn point doesn't seem to ever be used by the player (for respawn purposes), but is loaded when the player enters the Nether and is never unloaded until the player dies or logs back on.

I found this to be true on single player worlds, but have not tested it on multiplayer servers or realms.