Multiple CustomData : all data are not displayed in Contact Form

I've added a custom data : child, with multiple values.
This custom data contains 2 fields.
I've created a contact and added 4 children.
I can see these 4 children in the "view screen", but when I want to update the contact, only 2 children appear. If I click "add a new...", my 3rd child appears, if I click one more time "add a new...", my 4th child appears, and if I click one more time "add a new...", a blank form appears and I can add the 5th.