syntax error due to default value?

I have several form, and they all have an additional header
`Reply-To: [your-email]’

Only one of these forms gives a syntax error, and whatever I do, I cannot resolve the problem. Could it have to do with the fact that the field has a default? In the form I put a default for the logged-in user:
[email your-email default:user_email]

https://ww.wp.xz.cn/plugins/contact-form-7/