Paperwhite to Nexus 10 Whispersync Problem (Also Nexus 4 support)

Hi,

I'm trying to "Sync Furthest Page Read" from my Kindle Paperwhite to my Android Nexus 10.

The Process I'm using:

1. Import mobi file
2. Updated metadata from Internet
3. Reconvert mobi file
4. "Send to device" on Kindle Paperwhite
5. "Send to device" on Nexus 10

The problem:
"Sync to Furthest Page Read" is grayed out on the Kindle Paperwhite. I have tried turning automatic syncing on and off in the Kindle and it doesn't seem to make a difference. If I hit the sync button on the Nexus 10, it always says all devices are synced to furthest page read.

Any ideas?

P.S. Any chance of Nexus 4 support? Plugging it in (MTP) doesn't show the Device menu in Calibre.

Thanks!
Ben