Status Code 87 when trying to Validate Windows Server 2008 R2 Failover Cluster

Just came across this funky little error when trying to validate a cluster on Windows Server 2008 R2's Failover Cluster Manager.  In particular it comes up when attempting the "List All Disks" step.

"Clustering Validation check fails: Failed to prepare storage for testing on node ClusterNodeX Status 87"

Nothing really helpful shows up in the log files, and somewhat frustratingly only came across the solution by trial and error.  It seems that the tiny little boot partition at the start of the primary operating system disk (I think this is new with the Windows Build 6.1 Kernel [Windows Server 2008 R2]) does not have a drive letter assigned or mount point assigned.  Just assign a drive letter using diskmgmt.msc or diskpart for both nodes of your cluster and it will disappear and you will be able to validate.

There were other volumes that did not have a mountpoint or drive letter assigned, so I am assuming this error is specific to the primary disk.

Seems pretty silly, hope this is something that gets addressed by the upcoming Service Pack for Windows Server 2008 R2.