Azure B2C - Sign-in with non-English email addresses

We are using a custom sign-up/sign-in policy with Azure B2C and are having trouble trying to sign-in with foreign language email addresses.

We have followed the Microsoft tutorials and have used the custom starter XML files here.

We initially found that we couldn't even SIGN-UP with a foreign language email address (such as 伊伊伊伊伊伊伊@伊伊伊.伊伊伊) but we noticed that there was some regex in the TrustFrameworkBase.xml starter file that we could manipulate:

  <ClaimType Id="email">
    <DisplayName>Email Address</DisplayName>
    <DataType>string</DataType>
    <DefaultPartnerClaimTypes>
      <Protocol Name="OpenIdConnect" PartnerClaimType="email" />
    </DefaultPartnerClaimTypes>
    <UserHelpText>Email address that can be used to contact you.</UserHelpText>
    <UserInputType>TextBox</UserInputType>
    <Restriction>
      <Pattern RegularExpression="^[a-zA-Z0-9.!#$%&amp;'^_`{}~-]+@[a-zA-Z0-9-]+(?:\.[a-zA-Z0-9-]+)*$" HelpText="Please enter a valid email address." />
    </Restriction>
  </ClaimType>

So we changed the regular expression and we could sign-up!

But then, when we tried to sign-IN with the account we just signed-up with we got a message saying "Please enter a valid email address".

I've tried this with a vanilla sign-up/sign-in policy out-the-box and I get the same thing. There's a regex pattern attribute on the HTML text box that looks like:

      <input type="email" id="logonIdentifier" name="Username or email address" pattern="^[a-zA-Z0-9.!#$%&amp;’'*+/=?^_`{|}~-]+@[a-zA-Z0-9-]+(?:\.[a-zA-Z0-9-]+)*$" placeholder="Email Address" value="" tabindex="1">

that prevents sign-in.

If I go in and remove this pattern regex I can actually sign-in, so I know it CAN work. I just need to remove this pattern attribute.

I must be missing something. Can anyone tell me what I need to configure to be able to sign-in with such an email address?