Thanks for the replies back guys.
@charlie.it: I was more after where to look for the issue of sorting than for an issue in the SQL. 
@MTP: That helped a lot. I'd checked there a couple of times and noticed it only listed the grouping I'd made, but lacked the sorting I'd additionally added in when creating through the wizard (I've grouped two separate columns before sorting on a third). The fact it didn't show up this third column made me wonder whether it was even bothering to sort... so I manually changed the query it was based on and added the sorting on my own for all three columns and that seemed to resolve it.
This has puzzled me a lot though as to why there seems to be no way of changing sorting applied to non  grouped columns when creating it through the wizard. Is it that it never gets stored, or is there something I've missed in what the sorting and grouping does?
Thanks again for the help. 
