If you have a third party assembly that requires full trust for say a logging operation (This assembly does not have AllowPartiallyTrustedCallers).
You use this assembly through a custom assembly with AllowPartiallyTrustedCallers then deploy it to the GAC.
How can you use your custom assembly from low trust code when it’s dependency (third party assembly) issues security demands?
Note: Context is sharepoint.
Best guess : missing assert for security demands. Check out MSDN tutorial to get started. And SecurityPermission class for Assert method.