The latest update in the Synology Cloudstation client (mid Oct 2012) does indeed conflict with Dropbox upon startup. The conflict seems to happen when both clients try to index changes on the system at the same time. Upon startup, I stop the Synology one so Dropbox (which is more important for me) syncs its content. When it's done, I fire up the Synology client... The latter seems to be very buggy overall (unfortunately). It's in constant "sync" mode despite files already being sync'ed. Maybe Synology knows about this and is potentially fixing.
If a bug was found with Dropbox, it's most likely they'd fix it instantly as DB's user base if far bigger compared to Synology's. It's clearly something Synology should take a look...