The following works;
	
GridGroupByExpression groupBy = new GridGroupByExpression();
groupBy.Expression = "[Status] format \"Current {0}: {1}\" Group By Status DESC";
this.fundsGrid.MasterGridViewTemplate.GroupByExpressions.Add(groupBy);

The following doesnt work

GridGroupByExpression groupBy = new GridGroupByExpression();
groupBy.Expression = "[Status] format \"Current {0}: {1}\" Group By Status desc";
this.fundsGrid.MasterGridViewTemplate.GroupByExpressions.Add(groupBy);