A couple of things: what you have experienced is the same as a relevant number of other users experienced, and seems to be related to a problem which long predated DTTG3; it’s likely impossible to resolve. What DEVONtech have done is to mitigate the problem: even if you had had sync turned on, it would almost certainly have terminated with an error message rather than propagating the problem to your Mac. This safety measure was implemented quickly after the problem of so-called ghost files appeared.
Once you have resolved the problem once, I would not expect it to return. @OogieM’s report of continuous propagation is the first I have read, and I’m not convinced they are reporting the same problem or mechanism. I note they are using an individual WebDAV setup for example.
It’s not my job to restore your confidence in anything, and I’m not trying to make little of the issue; DEVONtech themselves were devastated when data loss occurred, although they did find a workaround which automatically restored files for many users. I was worried about the issue at the time; I no longer am. It seems reasonable to assume that the only reason you have experienced the problem now is your switch to DTTG3; it’s also reasonable to assume you won’t experience it again. Again: everybody would have been happier had it never occurred; no software can guarantee data safety, however - both hardware and software can fail. As such, a comprehensive backup-strategy is a must.
In addition to a backup strategy, I have implemented a checksum routine - the idea being that I could otherwise, in theory, miss that files have changed and that years later my backups might no longer cover the appropriate time period.
Precautions such as these are requisite, regardless of which company & software you entrust your data to. DEVONtech reacted quickly to the issue described in this thread. Mistakes, unfortunately, happen - but there is something to be said for trusting those who own up to them, rapidly mitigating what has happened.