TFS workfold /unmap "Multiple workspaces exist with the name XYZ"

This has been reported as a bug here: https://connect.microsoft.com/VisualStudio/feedback/details/574162/tf-workfold-unmap-not-accepting-collection-option

See here for a workaround: http://wiert.me/2012/08/29/vs2010-workfold-command-allows-moving-a-local-working-folder-for-a-workspace-but-not-unmapping-it-when-you-have-multiple-workspaces-with-the-same-name/