But maybe you want to check this with just a few of your contacts? If the syncing works for these edited contacts we can file a bug report
I have installed a new calendar and testet some different ways. The sync works fine in both ways (OwnCloud->Thunderbird and Thunderbird->Owncloud) when im using no pictures.
When im choosing "pics from my computer" in thunderbird it works only in thunderbird and the sync to owncloud fails (and never work again until im deleting all pics in thunderbird).
When im choosing "pics from web" it works in thunderbird and the sync to owncloud works, but i cant see the pic in owncloud and after the sync the pic is deleted in thunderbird too (maybe by owncloud).