There is an issue when defining field names that contain single quotes ('). This is particularly annoying for french usage of the add-on.
For example, a field named "Nom de l'utilisateur" (username) won't display correctly in the metadata of a post. There seems to be an extra escape char which renders the field as following: "Nom de l\'utilisateur".
First, I thought it was just a minor display bug and I could deal with it. However, after saving metadata of the post and reloading it, I found out it also affects the data loading: data is not displayed in its corresponding field as expected. However, it's correctly saved since I can see every value in the Custom Fields column in the Articles list.
Temporary solution: renaming the CTF fields and removing single quotes makes it work correctly.