Ok.... have you opened arctoolbox, spatial analyst toolset, kernel density tool (which is the link I sent). Is there not an option on the dialog for what you want? The help indicates some changes in pre 10.2.1 and post in how the calculations are performed... like search radius... This is obviously what is causing the difference and if you want to replicate what you previously saw, then you will have to do so. Did something appear as a default before usisng the similar dataset you had? Then you will have to emulate the default or provide an alternative. In short, there is nothing wrong with the tool, but more onus is being placed on the user to provide inputs to control outputs that meet their needs.
My reference to the code snippet was in reference to the assumption that there was no optional search radius being provided, as in the line was missing. skip this if you don't understand. But use the dialog and provide the inputs that you provided in previous years in order for comparison to be made.