Soft validation does not always work correct

I'm using the module in context of Drupal Commerce.

If a customer selects Country: "Austria", but provides a German VAT, a timeout happens and is being logged to watchdog correctly:

Typ vat_number
Datum Montag, 11. November 2013 - 13:32
Benutzer webksde-test
Standort http://example.com/checkout/xx/checkout
Referrer http://example.com/checkout/xx/checkout
Nachricht TIMEOUT
Schweregrad Fehler
Hostname xxxxxxx
Operationen

I'm not sure if this selection has something to do with the timeout, but the real problem is:
"Soft validation" is selected, but anyway the user cannot proceed. There are no error messages being output and the user just stays on the input form.