Forms: Not sending mail to customer due to single space in submit button in email address in field

I've got a couple of similar forms. All of them have both Email to Admin and Email to Customer enabled.
One single form did *not* send the message to the customer for unknown reason, but the Mail was sent to the "Admin Email Notification" "Email Address".

I finally seem to have found the problem: In this form's submit button, section "Customer Email Notification", the field "Email" had a trainling space after the otherwise correct email address.

The email fields in the form designer sould not accept trailing spaces, in fact the email address should be tested to be of valid form.

This is the relevant part as seen in the exported form:

"reply":{"enable":true,"email":"custom","custom-email":"This email address is being protected from spambots. You need JavaScript enabled to view it. ","subject":

I'm attaching the exported form as well (remove the .jpg from the uploaded file to get the xml file)

Regards
Peter