Just realised that this DOES work but ONLY if you use "Group By" feature.
Choose Group By Workspace or Tag
You can't drag onto the left side colum tags or workspaces.
You can drag Feng Office tasks into existing workspaces that have something already assigned.
You can drag Feng Office tasks onto tags which have something assigned or onto "unclassified" tag, but it shows an error sometimes. ( Query failed with message 'Unknown column 'unclassified' in 'where clause'' )