Apparent network issue with 4.3.18 on Yosemite host

[mikemini]

I am running an OS X Yosemite host with VB 4.3.16. I have a Solaris 11 VM that works fine. However when I upgrade to VB 4.3.18 I see erratic network behavior from the Solaris 11 VM. For example the Solaris 11 VM (which is the ZFS Simulator) serves NFS shares. When running on 4.3.16 these shares are accessible and can sustain a reasonable amount of IO. However when I upgrade to 4.3.18 even a simple file copy to an NFS share served by the guest times out and NFS Server Not Responding errors can be seen on the client. If I revert back to 4.3.16 everything returns to normal. So it would seem an issue was introduced with 4.3.18 at least on Yosemite hosts and Solaris 11 x64 guests. I have not tested this on other host operating environments. I should note that other guests seemed to be fine with 4.3.18 on the Yosemite host - but none of the other guests do much network IO. I apologize as I know this is somewhat vague but I have not had the opportunity to do more testing to see if I can narrow the issue down.