Cannot make use_strict_mode work with custom session handler upon 'files'

I want to implement custom session handler upon internal files handler 
similar to this: 
http://php.net/manual/en/class.sessionhandler.php#example-5380 (example 1).

But with session.use_strict_mode = 1.

I have been trying to test this sample code, but I can't seem to get it 
to work:

---
session_module_name('files');
ini_set('session.use_strict_mode', '1');

class MySessionHandler extends SessionHandler{}
session_set_save_handler(new MySessionHandler(), true);

session_start();
var_dump(session_id());
---

After delete an existing session file and rerun script, it create new 
file with the same id.

When there is no session_set_save_handler() it works as expected: new 
file is created with new id.

I suppose that it is a bug, but maybe there is a solution that I can't see.