Login fails when using return key

Hi

when I'm trying to login using the return key to send the login http request
it fails, but when using the login button everything works fine.

Tested it in Firefox, Safari and Chrome.

Does anyone know this strange behaviour?

Activating Webdeveloper Tools yields:
- when using the retun key the request for /index.php/login/auth.html?parameter.....
is aborted and no bytes are returned.
- when using the login button the request for /index.php/login/auth.html?parameter.....
is sent successfully and the following is returned:
Seite neu laden, um den Quelltext zu holen für: http://domain.tld/index.php/login/auth_html

My guess would be that something in Javascript aborts the request when using the
return key.

Has anyone seen this before?

Greetings

Oli4