Are you using Patch Management 6.x or 7.x?
In 7.x there is an option under the Jobs and Tasks section of your console. \Tasks\Jobs and Tasks\System Jobs and Tasks\Software\Patch Management\Import Patch Data for Windows:
Revise Software Update policies
Enable this option if you want the existing Software Update policies to be revised after the Import task has completed. Revising existing Software Update policies ensures that they are kept up to date with the latest files from the patch vendor, and fixes data integrity issues
If you have the first option checked, Revise software update policies, when Symantec detects that a patch inside a bulletin has been revised, it will become disabled. This gives you, the administrator, time to test that specific patch to make sure the revision does not cause problems in your environment.
If you do not wish for that behavior to happen, you can check the box that says Enable distribution of newly added Software Updates.
Next, there is an automation policy that can be enabled, to alert you when this action happens. That is located under Automation Policies and is called Software Update Advertisement Disabled.
If you're using Patch 6.x this behavior is still the same if you're using the Revise Software Update option on the PMImport section of your console. Unfortunately, you do not have the option to Enable distribution of newly added Software Updates.
Finally, it could be that when the software update policy was being created, the individual patches were unchecked.