I'm having the problem with all Office documents on an iMac running Mavericks and Office 2011. The files are stored on a Linux fileserver using Samba. Not a Synology problem, we don't have any Synology kit.
I would say it is down to MS Office or OS X, although given this problem has existed over 3 versions of OS X now, it is either a really poor showing by Apple or the bug is Microsoft.
That said, there was a post at the end of page one, which said "users diconnecting from the network without closing," the iMac loses its connection to the network when the screen goes black after 10 minutes of idling. This often means that the shares have disappeared and I have to use FInder-> Go To Server to "wake up" the connection again.
Edit: Oops, just seen I replied to the wrong post...
One other thing, I did notice that a temporary Office files was sitting in the directory, when I tried to open the file. It doesn't seem to bother Office on Windows though.
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