MPG has never trusted Finder file copy across a network, having observed failures to copy changed items, as well as total-death system lockups more than once in past OS X releases.
Today I observed the OS X Finder copy a file to my other machine, delivering a zero-byte result after a short pause: no report of error and the normal sound played at the end of the copy. In short, total data loss (of the copy) with no warning whatsoever. Fortunately I had the original but had a move been done (by holding down the command key while dragging), the file would have been lost.
This was using WiFi; MPG normally uses only gigabit ethernet, but the MBP is short one Thunderbolt port while testing, until the OWC Thunderbolt 2 Dock arrives.
* Network failures with WiFi are not uncommon; any file copying algorithm has to assume that a failure could occur, and report the error!