Invalid character set on confirmation email

I'm having an issue when submitting confirmation emails with a custom record summary. All "spanish characters" or characters typed using an spanish keyboard (such as : or - which are placed differently than the english keyboard) come with weird characters (as in "A4: Aviación" or "1:500") on the custom record summary I have set to be attached to the confirmation email. And that only for the values submitted using a subform, characters from labels and paragraphs look ok. So it looks like the the characters imported from subforms are not properly coded.

I don't know if I made myself clear. Sorry about that. See attached file for an screencast of the confirmation email.

Thanks in advance.