I sometimes have trouble syncing between my KF and my two E Ink Kindles, for no apparent reason I may add. My K3 syncs well with my K4 and both sync well with K4PC. Neither K3 nor K4 play nice with the KF though, or vice versa. The KF does sync well with K4PC. The common factor for sync booboos seems clearly to be the KF, so I'm thinking there might be a FW issue. If I keep trying to sync, doing manual syncs, then it will ultimately sync, but it is sure not doing it fast or automatically or consistently.