Camera backup deleted files on my backup server

[decoherent]

My phone's storage has filled up, so I opted to use Google Photo's option to delete local files from the device. I've had Sync setup on my phone with the built-in Camera backup to my Linux server. However, when Photos deleted the local files, Sync deleted them from the server as well! From what I read in the documentation, this shouldn't happen, nor did it happen when I tested deleting some photos on the phone ahead of time. This isn't quite catastrophic, as I keep versioned backups of my camera folder, but it's pretty bad. Why did Sync do this? How can I prevent it from doing it again in the future?

edit- to expand on this, sync moved all of the files to "/srv/sync/camera/.sync/Archive/Camera". It's been caught by my other backup (Crashplan), but this is pretty bad.

edit 2- Ah crap, now I see that the share on my server had "Overwrite any changed files" checked. Am I correct in understanding that this is what the problem was? I tried to copy a file back into the sync directory on the server. When that option is checked, Sync instantly deletes it. When it's unchecked, it seems to leave it alone. So I should be able to just move all of the files in .sync/Archive back into my normal directory on the server, and Sync will leave them alone, now and in the future?

[Gane O'dwyer]

@decoherent The option 'Overwrite any changed files'. If enabled, Sync will do the following: 

1) renamed file in an RO folder will remain there. Besides, the same file with an older name will be re-downloaded
2) deleted file will be restored
3) edited file (changed content) will revert to the most recent version supplied by a RW peer
4) added file will not be deleted, nor will it be synced.

And Remember that in case of data backup (backup makes use of RO folders), deleting files on your mobile device will NOT delete them on the backup device. Are you sure that the Camear backup option was used on your side?

Could you send a screenshot?