Creating a user account using the "Create account" link at the top doesn't create a sandbox account.
A common user scenario for this is the case of calls-to-action in blog posts or emails that invite people to translate a project by linking directly to Special:Translate. Creating an account using the top link doesn't put the new account in the sandbox, but creates a usual account without translator permission.
Clicking the link for getting a permission under the editor in the TUX interface brings the user Special:MainPage, and then clicking the green Translate button on the main page brings the user again to Special:Translate and not to the stash. This is confusing and at least one user complained about this.
(All of the above was tested in translatewiki.net.)
Version: unspecified
Severity: enhancement
Whiteboard: leteam?