Are you wanting it to sync? You can turn Whispersync off and it will stop automatically syncing and will only do so when you manually tell it to.
To switch off the automatic sync between devices:
1. go to Amazon.com and visit the Manage Your Kindle page
in your account settings.
2. Scroll down to and select "Manage synchronization between devices."
3. Select "Turn Synchronization off."
Once you turn synchronization off, your books will still open to the last page read on that device, but Whispersync will no longer automatically sync bookmarks or the furthest page read with other devices, unless you wish to sync the book manually, by which you can press the Menu button and select "Sync to Furthest Page Read."
...also, if you turn WiFi/3G off on a device, it won't be able to sync until you turn it back on again.