Data stored in JSF flash during a request is not returned in the next request. It's returned during the 3rd request. I have a very simple test to verify this behavior.

LoginBackingBean has two methods which are called in 2 subsequent requests. Variable kept in flash memory during request 1 doesn't return in request 2 but in request 3.

3 small files required to reproduce are attached. First referer.xhtml should be opened in a JSF app, then its login button calls doLogin method and takes you to Login.xhtml file. Now "Simulate Login" button need to be clicked twice to get the variable.