Have a Q1900 also, running DSM5.0 4493 update 5, Nanoboot-5.0.2.4 DSM 5.0-4482. Same type of problem.
Appears to be worst when moving a file from nas to nas trough external PC, hangs after a couple of seconds.
So I select cut in windows explorer, move to another directory and do a paste.
When just moving files to and from NAS it appears to be OK.
As some people do not have the problem, maybe a BIOS setting that is causing the problem?