Dropbox Sync \ Corrupting Pdf Files

ReadyNAS Model 628X with firmware 6.10.1 (latest)

Sync to Dropbox (every 30 sec) was causing the files to be corrupted coming into the NAS from a FTP server. Some files were fine and some files were getting corrupted, the file size was 0KB.

I think the file was downloading and at the same time DROPBOX was trying to sync and it was maybe putting a lock on the file which was causing my FTP script to fail and thus causing the file corruption. 

Should there be something like till the files gets downloaded in whole the drop box sync should not start.

Please check.