If you click on "Edit" on a case and click on "Save" without changing anything on the incident, the last modified date is updated to the date/time you click on the "Save" button.
This is actually incorrect as no modifications were made.
Response from CA Support ..................
I have confirmed that the behavior is as per the design, having been present in the product at least from version 11.2 and up through the current version 14 cum#1.
I have also confirmed that the behavior is consistent for Incident, Problem, Request, Contact, Organization, Location, Site, Group records, all of which include a Date Modified field in the out-of-the-box detail form.