It seems that type="email" content is not correctly converted to punycode, so a user using a doublebyte name is unable to submit the form. Worse, there is no UI for this error, so the user has no idea why the form hasn’t submitted. It appears as if the submit button isn’t connected to anything.
Ref: http://code.google.com/p/chromium/issues/detail?id=45804 for a related Chromium bug on the lack of UI for validation errors
note a doublebyte domain name is correctly converted to punycode for type="url"
Bug 40747 is about the UI, so this may as well be repurposed to be only about not accepting IDNs. E-mail inputs should certainly accept IDNs and convert to punycode for submission -- it only makes sense. The spec mentions this as an example but doesn't require it (since it's a UI issue):
"User agents may transform the value for display and editing (e.g. converting punycode in the value to IDN in the display and vice versa)." <http://www.whatwg.org/specs/web-apps/current-work/multipage/states-of-the-type-attribute.html#e-mail-state>
Change URL to test case:
Here is original URI in URL field:
Created attachment 167019 [details]
Proof of concept