We have a SP2010 site that we are making extensive use of the CQWP (Content Query Web Part) on. When I point the CQWP at a specific list it displays description value fine. The problem is when I point it at a hierarchy of SPWebs and configure it to rollup all items of type Calendar. When I do this all data comes through fine except for Description, which is very odd. I tried using internal field name too it doesn't seem to make any difference.
So my question is how do I get CQWP to render description field from multiple calendar lists?
I was able to get this working by changing the DataMappings, and DataMappingViewFields. The values in these fields are very sensitive and a space or semi-colon in the wrong place will break it. I've posted what worked below, hopefully this will save someone else two days of misery!