default:post_meta not working

Hi there. According to the documentation it should be possible to get a text input default value from post_meta if set in the page calling the form withdefault:post_meta.
I have a custom meta set with the key being the same as the field’s name and the value holding the default value. Unfortunately it doesn’t work with my setup. Anyone experiencing the same?

https://www.ads-software.com/plugins/contact-form-7/