Web Login - failed to detect a username / password field

On the Asana login - https://app.asana.com/-/login

The plugin offers to save the username and password and does this correctly. After visiting the site again, the plugin detects the address and offers to fill in username and password, but does not do it.

Manually adding the element ID's of the username field (email_input) and password field (password_input) seems to have fixed it.

I'm just wondering why the plugin can detect the fields correctly and save them in the first place, but afterwards I need to manually define the fields to fill out.