Hello,
I have a similar problem.
I shared a virtual disk between two machines Windows server 2012 R2 with the option of "multi-writer", but I have the problem when I save a file from a virtual machine in the disk it does not appear inmediately in the other machine. I need restart the machine for I can to see the file.
These machines must be operational the 24 hours, so I can not restart. What I can do to see the file that I save from one machine in the other immediately?