I agree. The only reason I can think of that this can happen is if the file is moved while still running, and then a new file is created at the old location with touch.
And that would only work until syslogd was restarted; aftwards it would write to the proper place again.
So you might try using find to see if there's another copy of the file on the system, and/or you might try restarting syslogd.