I can still reproduce in 15.9. The reason is simply that, as a feature, the login redirects back to where it was when clicking the login link and the simplest for that was to put the xredirect right in URL generated for the link parameter generated.

I guess to fix this, we would need to inject the xredirect parameter in javascript at the moment the button is clicked. Another possibility is to disable that feature when action==export (since, whatever the export, it does not make much sense to redirect to an export after a login).