I'm running 8.,1 Enterprise on a new system with an NTFS SSD boot disk (C:) and a Mirroed ReFS Storage Space data volume (E:).
I tried to drag a very small text file from my Desktop to a remote 2003 Server share opened in Windows Explorer and got an error dialog:
File Too Large
I copied this text file to a folder on my C: drive and then tried to drag it from there to the shared folder, and it worked.
There are also no issues copying from the ReFS volume to a 2008 R2 share.
I hope this can get fixed soon because it's really going to impact my workflow.