Hello
You may remember that some time ago I published a web post regarding output cache stops working after installing MS11-110:
Like I pointed SharePoint 2010 April 2012 CU fixes that issue. The public info regarding that change has been publishing on the following KB:
http://support.microsoft.com/kb/2714963
I hope it will be useful for you.
Kind Regards.
Héctor Calvarro Martín. SharePoint Dev. Microsoft Support Engineer for DEV EMEA