Filling comb text field

[AelyPro]

Hello, we are trying to use PdfSharp to fill a pdf document. It's working fine except when we need to fill comb type field.
When we fill them, they appear wrongly, each character are next to another like if it wasn't a comb field. Like in this image

When we click on the field it appear the right way :

From what I found during my search, you need to specifiy the right value for the property "/Ff" for a field to be a comb. This value is correctly fill on our field. Here are all its properties :
.

And here is how we fill the field with our text :

(pdfDocument.AcroForm.Fields["D1A_naissance"] as PdfTextField).Text = "10061939";

I'm realy lost, any help would be usefull !