Security : SQL Server Object Access From One Schema to another schema
The concept you want to understand is called "ownership chaining"

As long as the owner of the object and database remain the same, SQL Server will not re-evaluate the permissions of a user after the 1st object in the chain.

In your first example you denied USER1 access to TABLE1 but allowed access to VW_TABLE1.  Since USER1 has access to VW_TABLE1 and the ownership chain has not been broken, they can see TABLE1 because permissions are not re-evaluated inside the VIEW.

In your second example I'm assuming the SEC schema must have a different owner which causes SQL Server to re-evaluate permissions when inside the VW_TABLE1 view.  

In short, to fix this problem make sure all objects have the same owner