We have customized content query web part by using custom header style xslt and item style xslt which are configured using properties 'HeaderXslLink' and 'ItemXslLink' respectively.
Also we are grouping data by categories using 'GroupBy' property.
Output of cqwp is as below.
Group header 1
Group header 2
and so one.
Prior to installing OCT CU 2012 this functionality was working as expected. However after installing CU now Group Header is not shown. We have upgraded server from JUNE 2012 CU to OCT 2012 CU.
This is consistent behaviour on all the servers where OCT CU 2012 is installed.